figure out if i'm pregnant...?

I am only fifteen and I am using the birth contorl method but I have been late on it three times and I didn’t take it yesterday. And about two days ago my boyfriend and I had sex twice without a condom. I’m pretty scared I don’t know what to do. I haven’t had my period yet I mean it’s always been irregular but it hasn’t ever been this late. And I don’t have money to buy a pregnancy test I’m scared. I’ve had a lot of belly pain and back pain i get nausus easily and i’ve been eating and peeing a lot. Someone please help me