Could also have been part of your mucus plug
Call Ur dr!!! Ur 38 wks U can go into labor at any point. My last 2 babies were born at 37/38 wks.
Yeah I'm not allowed to have sex due to mild bleeding... usually it just means the cervix bleeds easily when irritated. I would let your dr know, they'll probably warn you to stay away from intercourse for a little while just incase.
Just call your doctor and let them know, but bleeding after sex is normal so don't freak out to much