Please answer asap?

i have had 3 childeren. my last was 2 years ago but ever since having him havng can be painfull. if my partener goes to deep i get a really bad pain in my stomach like ive been punched. it wasnt like that b4 having my last child and was wondering what could be causing it. im never in pain unless having and its becoming a problem as any other position other than misionary causes bad pain , is there any chance my womb could of dropped or anything or is this normal after having 3 children?