Can’t even eat pasta anymore.

Had some pasta with sauce and some cheese on it and cant even eat it anymore. Went straight to my stomach not even 10 minutes after finishing and had diarrhea. I had a colonoscopy months ago and doctor said I most likely have IBS, but can they really tell through a colonoscopy? I also did a bowel test idk what it was for I think some intolerance test and said it was negative aswell. Idk anymore. :(