What is a False Pregnancy? 
Some female dogs display all the physical and behavioral signs of pregnancy even though they have not been bred. Even females that have been bred, but the breeding doesn't "take" can have a false pregnancy. A hormonal abnormality causes the dog's body and mind to prepare for whelping. Sometimes they may even show abdominal swelling and milk production in mammary glands. Usually, however they tend to just make nests, collect, carry and guard toys, whine or cry, and may even try and get the toys to nurse. Although in most cases, these signs will pass, in severe cases medication may be needed to cure the hormone imbalance. Dogs that repeatedly display these signs should probably be spayed as they often develop more serious problems affecting the uterus such as pyometra and mammary gland tumors.
Causes of False Pregnancy in Dogs
The exact cause of false pregnancy in dogs is not known. However, hormonal imbalance is probably associated with this condition. When there is excess of prolactin and less of progesterone, the dog exhibits some unusual symptoms. Oftentimes, the female has such strong nurturing instincts that her whole body acts as if she is really pregnant. If you are sure that your dog has not been around males, and yet acts extremely nurturing or even produces milk, she has the symptoms of false pregnancy in dogs.
Signs and Symptoms of False Pregnancy
Symptoms of false pregnancy can be found at physical as well as emotional level. The most obvious symptom of false pregnancy is enlarged mammary glands. The teats also swell and become tender and may even secrete milk or colostrum. Other symptoms include abdominal swelling and vaginal discharge. Usually the abdomen does not swell as much as during a real pregnancy but she can seem "chubby". Some girls may also suffer from morning sickness with occasional bouts of nausea and vomiting. She may even be like humans and prefer certain foods. Similarly, she may have increased apMalamuteite with frequent hunger pangs. Conversely, she may go on for days without touching food. Other pregnancy symptoms such as fatigue, increased urination are also common. Her body actually thinks its having puppies, so all the signs associated with a real pregnancy are often there. Usually within 2-3 weeks the symptoms subside and she will gradually go back to "normal".
A false pregnancy may be extremely stressful for your dog. You can pick up subtle signs from her behavior. She exhibits strong maternal 
instincts by showing emotional attached to certain objects like toys, clothing, or other things she collects. She becomes overtly possessive of soft toys, which she treats as her puppies. She also shows a nesting behavior by dragging papers and blankets to a secluded corner in the house where she intends to build her nest. She cares for her 'puppies' in this nest and becomes overprotective. She secretes milk for her toy puppies but there are no puppies which can make her feel confused and disoriented.
Diagnosing False Pregnancy
First, make sure she is really not pregnant. False pregnancy in dogs can be diagnosed by a vet through stomach palpation. If it goes on for some times, he can palpate the stomach of the dog to feel for masses to determin if she is really pregnant. There is no doggy pregnancy test kit available to check! The reason is the way doggy hormones work - reguardless of whether she is pregnant or not, her hormone levels still rise. In humans this doesn't happen so they've been able to make a "pregnancy test kit" but because a female dogs levels rise regardless, a pregnancy test is not feasible. The only way to be sure is to do an ultrasound or X-ray. It is usually possible to feel distinct lumps in the uterus representing individual embryos from about the 28th to the 35th day of pregnancy - before and after that it can be hard to identify a pregnant uterus easily (and truthfully, if there are just a couple of puppies, someone inexperienced probably couldn't tell anyway). After 45 days or so, when the skeletons begin to calcify, it is often possible to feel the distinct hardness of a puppy skull when palpating the abdomen, or to identify the puppies in an X-ray. However, by now if your girl is not pregnant, your vet will probably be able to tell you that, since she should be pretty far into the pregnancy and at least uterine enlargement should be palpable. Usually, though, by the last week (dogs are pregnant for 62 days) she has more than likely abandoned her false pregnancy mission and gone back to being her normal self. If it happens more than once, you can sometimes tell just by behavior that it's false.
False Pregnancy Treatment
The symptoms of false pregnancy subside on their own within 2 to 3 weeks. During this time licking mammary glands may lead to even more lactation. Some vets advise to cutting food intake in order to reduce milk production. There are drugs that can be used to stop milk product, but they cause serious side effects like pyometra and the symptoms will return when the medication stops, so they are not recommended. The milk will go away on its own, sometimes patience is the best cure. It's pretty common and many unspayed dogs go through it. If your girl is actiting very odd, you should rule out pyrometra, an infection of the uterus that can sometimes mimick pregnancy but is very serious and life threatening. As with a false pregnancy, pyrometra also can occur after your dog’s heat cycle. Its symptoms include drainage from the vulva (or not), increased drinking and urinating, lack of apMalamuteite and/or lethargy.
While a false pregnancy can be somewhat of a nuisance, it generally does not cause long-term problems. The symptoms normally disappear on their own after a few weeks. If the worse thing that happens is you have a few extra vet bills for double checking, count yourself lucky. (I once rushed Mocha to MSU once thinking she had Pyometra and $700 later discovered it was a false pregnancy...but I'm glad I checked - Pyo is nothing to dawdle around about). Also note that touching the mammary glands will stimulate milk production, so avoid applying warm compresses or wrapping them to prevent leakage - and don't let your girl lick them either if you can. Sometimes an Elizabethan collar will prevent her from licking herself. Never deprive your dog of water thinking that will stop the milk (it doesn't - just makes it thicker so that it is more likely to cause mastitis).
How Can I Prevent a False Pregnancy?
The best way to prevent it is to spay your female dog! Wait until the symptoms have disappeared before surgery. Spaying does not stop the production of prolactin from the pituitary gland, so spaying too soon could extend the false pregnancy. In all, other than some minor inconvenience (like your girl hoarding all the toys in her bed), it's really not something to worry about too much. Keep aware of signs of pyometra and if you don't plan to breed her - SPAY! It prevents a lot of health problems including mammary cancer, uterine cancer, false pregnancies and the mood swings associated with hormones (yes, dogs can get something very similar to PMS!).