should i see the Dr?

cor the past week or two everytime my husband and i have sex I am in a lot of pain. like a lot a lot. my whole pelvic area and half my stomach hurts like hell and i just wanna cry. the only thing That's changed with my husband and i is that about a month ago we started messing around with another couple. ever aince then my periods have been all out of whck and ive been in a lot of pelvic pain randomly especially after sex.