About 2 almost 3 weeks ago I had my period, and every since about 1 1/2 weeks ago my breast became sore, it hurts to sleep on my belly, why?

It could be that you're getting your period, could be that your bra is too tight, it could be any number of things.

We really can't tell you if you're pregnant or not, or if there's something else going on. A diagnosis isn't possible over the internet.

Wait and see. If your period is late then try taking an hpt or go to the doctor for a blood test.

That's really the only way to find out for sure.

Good luck.