What Are The Chances Of Pregnancy After Taking Pill?

I had unprotected sex with me boyfriend. It wasn't even really sex, he basically put it in and then took it out. He ejaculated over the night and late the next morning he put it in and out of me again (both these times we unprotected). I am on the pill but had been kind of unreliable at taking it. I am meant to take it at about 10 at night but i sometimes forget and take it first thing in the morning. I had been on it correctly for at least four days before the sex. Is it possible i could be pregnant? If yes, how do I find out a definite answer? Thank you in advance for your help.