Was very constipated recently, had sex, and after a while it hurt. is the constipation in relation to the stomach pain during sex?

No way to know here: Sorry, but we don't know your specific circumstances to be helpful here--how severe ; acute is your constipation, ; if present what's it's cause? Is there an underlying pelvic inflammatory process? What accompanying signs may be present (bleeding, tenderness, discharge) or do you have an underlying problem (colovaginal fistula, infection, colitis, etc.). Your doctor knows you best--call him/her.