Hello,
Without examination,confirming a diagnosis is tough but your symptoms are suggestive of infectious mononucleosis,irritable bowel syndrome and inflammatory bowel disease.
Infectious mononucleosis is caused by EBV(Epstein barre virus ) and is characterized by fever, sore throat, muscle soreness,diarrhea ,abdominal pain and fatigue.The important thing is that the virus lies dormant in the B cells indefinitely after symptoms have disappeared, and resurface at a later date.
Irritable bowel syndrome (IBS) is a functional bowel disorder characterized by mild to severe abdominal pain, discomfort, bloating and alteration of bowel habits.
Inflammatory bowel disease (IBD) is a group of inflammatory conditions of the large intestine and small intestine. The major types of IBD are Crohn's disease and ulcerative colitis.
I sincerely advise you to consult a physician and get these three possibilities evaluated.Monospot tests,immnuoflorescence, antibody titres,colonoscopy and CT abdomen are needed to confirm a diagnosis.
Hope it helps.Take care and pls do keep me posted on how you are doing or if you have any additional doubts.
Did your doctor run a blood test? 3 years is an awful long time, but mono can be a doozey (though I have never heard of anyone having mono for more than a few months...)