Pregnancy or not ?! neeeddd tooo reach outt

Well my boyfriend and I had sex about 3 weeks ago, on march 31, and again on April 1. It was our first time too.We used a condom and it did not break, there were no scratches or anything. My boyfriend said it did not slip off, but when he pulled his penis out it was basically around the head, so i kinda trust him. It didnt completely slip off. Yet, i'm still worried! I got my period a week later, on April 9, and it should be gone by tomorrow, April 16. My period usually lasts about a week. Right now I am REALLY WORRIED. I don't know if i'm pregnant or not, and I don't wanna talk to anyone else about this. My stomachs been feeling queezy and nauseous, but i'm not so sure. I've also got headaches a few times but i think it may have to do with stress from school or lack of productivity. (Spring Break, have done nothing). I've also done a few exercises trying to get abs, such as sit-ups. And when i rub my stomach, i feel something, but it may be the intestines or stomach that i'm feeling. So basically, it feels kinda hard, when I point it. Could this be due to sit-ups? Well, all I know is I"M JUST REALLY WORRIED. AND HOPE THAT IM NOT PREGNANT. Please, someone tell me& help me! Advices?