I agree with SassyLassie. Also, it might be endometriosis. It is very common and can cause chronic abdominal distention. It can't be seen on a CT scan or ultrasound. Look up the symptoms and ask a doctor.
Hello,
Has your gyn done any ultra sounds to see if this is ovarian or other female organ, related. It does not have to be cancer, even benign growths can cause some tummy swelling at times. I would see another gyn and ask for some tests.
In the meantime, yes, try taking a good, high potency probiotic to put the friendly bacteria in your tummy. Cut all gluten containing foods to see if this helps also.