With ibs-c is it normal to have a slight burn while defecating? not painful one, just slight one. no blood on stool/tp. doesn't hurt wiping after.

Yes: Yes with ibs-c you can have some rectal discomfort or burning

Not usually: IBS usually causes intermittent crampy pain in lower abdominal region. The burning could be caused by the food you eat and/or irritation one or two inches up in the rectum. I'm sure you have had colonoscopy but it may pay to have your physician do a proctoscopic exam to delineate the rectum. Much more comfortable than a colonoscopy.