Cramps during sex and brown/red discharge. I’m on birth control and don’t get a period.

Pain or cramps during intercourse activities can b understood because for some it happens due to Un-fitness, non flexible physic. Sudden deep moments like pressure on lower back, push on inner thighs, and other joints. legs spreading beyond expansion limit, etc.
But i have no idea for red blood discharge, may be it could be periods got started during intimacy session, or something other medical issue which only the doctor can explain better then everyone else.