Just some ideas to help you,
Suggest discussing with your doc when you are really bloated if a plain abdo Xray may show something, like mega colon etc. or adhesions from previous surgery, or just by chance. Especially since you mention you are worse after exercise, so maybe something is tugging.I am guessing your tum is now bigger than other family members. I am one of those strange folk where an ultrasound cant even pick up a second baby, but a plain abdo Xray noted my different intestinal problems, maybe you are in that group!
Some 'words' you might like to look up are gastroparesis, CIPO [https://rarediseases.info.nih.gov/diseases/12744/chronic-intestinal-pseudoobstruction ]
and good old IBS. The support group sounds good, and I hope it helps you. IF the rest of your body is normal size, then it seems unfair for you to have to diet, to try and lose girth. I fully agree with the dietary journal, as that helped me often find the culprit of severe pain etc.