Painful sex..how concerned should I be?

I am 7dpo and my bf and I were BD tonight and it hurt my lower back so bad we had to switch positions but then it made me have cramps so bad that it felt like my period was coming. I've never had this except when my period is actually here like that day. I'm due sometime next week. I took clomid this cycle to try to get pregnant and I know I ovulated but now I'm starting to lose hope like why would I be feeling like my period is coming on like this?