Ghilly is so right about the link between a history of false pregnancy and the often-deadly womb infection, "Pyometra".
I can attest to this because my own dog had a history of mild false pregnancies. They never seemed to bother or distress her at all, and she was always a super fit and healthy dog.
She developed Pyometra age 13. If I hadn't been aware, and got her to the vet very quickly, I could have lost her. It was a true emergency situation, and the only symptoms she showed were: a lethargy which crept up over a couple of hours...and a slight white mucussy vaginal discharge (which smelled perfectly sweet!)
So you see -there weren't even any obvious signs an infection was raging inside her.
She had even eaten her breakfast that morning! And been for a happy walk! Her symptoms started creeping up from about midday. By 2 pm I knew something was wrong.
By the time I got her to the vet, she was already 'toxic' so the vet told me, had a fever, and needed antibiotic and fluid IV before he would even attempt surgery. She was operated on early the next morning and was okay, and regained her fitness and health afterwards.
But I am aware it doesn't always end like that. Many otherwise healthy dogs die from Pyometra.
There really only ever IS one real solution or protection, and that is (if the dog is fit and well anyway) to have her spayed.
The problems with false pregnancy in dogs is that once they have one, they are prone to having others. While it seems harmless enough, it can be psychologically traumatic for them as they search for puppies that don't exist, and if they produce a large amount of milk, they can develop mastitis.
There also appears to be a link between false pregnancy and pyometra, a life-threatening infection of the uterus. Signs of pyometra present within three weeks of a heat cycle or of a false pregnancy or the whelping of a litter.
Since your dog seems so prone to them, unless she is an absolutely superlative representative of her breed being kept intact for the purpose of breeding more champions, the safest route to take in her case would be to have her spayed as soon as possible. This will stop her false pregnancies and allow her to simply enjoy being your lovable pet instead of going through the angst of wondering where her (nonexistent) puppies are and producing milk to feed them and going through all the worry of nesting and expecting babies that are never coming.
Ghilly
However it is often so that a female with a history of False Pregnancy can be more prone to developing Pyometra or problems with the breasts, including breast lumps.
The excess weight is either: because she had "nesting" behaviour during the False Pregnancy, and wasn't inclined to get much exercise outside....or is water retention, caused by her hormones. BUT it could be something else entirely. Other conditions also cause unexplained weight gain which are not directly food/exercise related.
The best treatment is healthy food, good exercise, distractions such as games etc, which will stop her brooding, and time of course, because this condition passes.
However it will no doubt recur. There really IS only one "treatment" which will totally stop this happening and that is having her spayed.
But, if you are interested in trying an alternative remedy, some people have had good results with homeopathic medicines which are quite safe for dogs and don't need a veterinary prescription. Pulsatilla, and also Sepia are remedies most often used for false Pregnancy. If you want to go down that road completely with your dog, you may be able to find a holistic or homeopathic vet in your area?
In my experience, homeopathic remedies either don't work at all, or work in the most astounding and quick way with dogs, and with no side effects.