Distended Abdomen, Exercise Regularly, Good Diet, No Help. Advice?

As a 56 year old female, I have spent the last 6 years battling a chronic distended abdomen. I have had every test known to man and no one can pinpoint what is causing the constant swelling of my abdomen. My previous (retired) gastroenterologist diagnosed IBS , which I personally think is what they say when they don t know what the problem is. I eat very little and try to stick to fruits and veggies and lean meats. I eat small meals and avoid fried or fatty foods. I drink mostly water and either chamoille or peppermint tea to help with bloating and gas. I have recently been drinking protein shakes with fruit for 2 meals and eating one small meal. I try to walk regularly and do Zumba. I have to wear clothes two sizes too large to go around my waist . I am so tired of looking pregnant and being miserable. I told my allergist (who I went to for testing for food allergies ...of which I have none) that I was giving up after this summer. I have spent thousands of dollars and though different doctors have tried, I feel the medical profession has let me down. I teach school and during the summer my problem was, while not gone, better. I have been back in school now a week and and I came home today with a HUGE adomen. I am tired of crying every night with no solution. Any advice would be appreciated.