Pain in my lower abdomen

Me and my bf are sexually active and he's been finishing inside me on & off for about a month now.. last night we had sex and it was painful because I've been having this sharp pain in my right lower part of my stomach and I woke up today with the worse pain I cant even move certain ways. What could this be.. my last cycle was late a good 8 days & I never been late before.. sometimes early but never late. Any ideas?