I have all those symptoms you do. I try not to push on my left side anymore, I used to wonder if I did if it would hurt, it does so I just leave it alone. If I were you I would see a Gastroenterologist and get a colonoscopy asap. I have all those symptoms but also a lotof rectal bleeding, up to 30 bms a day, bloody diarrhea or mucus to go along with all the things you stated.
Diagnosed with Left-sided UC in 1995 at age 15,
Prednisone, Rowasa & Hydrocort. Enemas, Proctofoam, Sulfasalazine, Asacol, Probiotics, Fish Oil, Aloe Juice, Canasa, Enotcort, Colazol, Anamantle, Remicade, etc... had 1 inch deep rectal ulcer 2004, put on Remicade, August 2007:Increased Remicade dosage-700mg every 6 weeks,diagnosed w/ Psoriatic Arthritis & Fibromyalgia Current meds: Clorazepate, Lomotil, Tylenol pm, Lyrica started 1/17/08, Humira started 4/4/08