Shut up and look pretty. Should I be having sex on my period? And don't be concerned if you see dark red or brown clumps during or after sex; that's just older blood and cells of your uterine lining, and it's perfectly normal. To avoid stained sheets her patients' biggest concern , she recommends putting a towel down on the bed, or getting busy in the shower. She knows a thing or two about slut shaming.