You are feeling at your wits end --- very understandably.
You refer to a "my doctor" in your post. IS this Physician the only Dr. you have consulted over this issue? If so, (IMHO) it is high time, (actually, it's well beyond high time) that you seek the opinion of another physician elsewhere.
If you have had multiple exams with no finding of any organic bowel disease, the diagnosis will always be Irritable Bowel Disease (that means assigning a functional cause to your complaints) because they simply can't find evidence of any organic cause.
However, G.I. practitioners can vary greatly in their experience level, especially within the spectrum of the Inflammatory Bowel Diseases. I take the liberty of assuming something here --- I assume that you have had a colonoscopy which was reported out as negative (i.e. normal). ?Possibly you have had multiple colonoscopies -- with that same outcome? Were biopsies taken from throughout the entire colon on each and every exam? If not – why not?? If taken, --- where were they read and reported out, and by whom?
Time to venture out to seek out a different G.I. Doc. Look for a Doc. that states to having a special focus and interest in the Inflammatory Bowel Diseases. Probably either down in the Boston area, or perhaps in New Hampshire.
You might run through this list of recommended Doc,s to see if you can find a Doc. in some fair proximity to you.
Best of luck, let us know what you can find.