Worried!

I'm a 37 yr old female and I have some concerns I'm not sure how to address. I had basically diagnosed myself with IBS for yrs now and i've been overlooking changes in my bowel habits. For years now I've had what I consider diarrhea, mostly right after I eat, its been getting increasingly worse. In the last couple of weeks, I've had unusual shape stools. I believe its described as ribbon like stool. Today I feel constipated and bloated, had a very small bm that cause alot of straining and pain, little dull gnawing pain in my left abdomen area, and I feel a little nauseous. I did have a colonoscopy several yrs back with a removal of a polyp, haven't been back to the doctor with it since. Do I have reason to be concern?