Virginity

So I had sex 4 days ago for the first time and I’ve Done it for 6 times now (over 2 days). The first one was painful, 2nd one not painful but very uncomfortable. 3 and 4 uncomfortable. 4-6th times he can keep thrusting but I still feel very uncomfortable and a bit pain. Also The pain I feel it in my bumm like a tiny cramp like pain. Why do I feel pain in my bum? I stopped having sex yesterday and today cause I got my period .