super bad lower tummy pain

So me and my boyfriend were having sex and i was laying flat down on my stomach and he was behind me, he's pretty big if it matters or not but anyways as we were going 10 minutes in my stomach started KILLING me, we had to stop and the pain wouldn't go away. It's below my stomach type of pain it hurts sooo bad and it's been hurting all day and we had Sex when it happened last night. It hurt so bad I could barely walk when it first happened. He busts in me all the time and I'm on the pill. Could it be a sign of pregnancy or just bruising ? Please help I'm freaking out