Potential Pregnancy? I need advice

I had sex for the first time last night and it was with out a condom. I'm almost positive he pulled out in Time but I'm paranoid there may be something wrong. I have a very irregular period about 50 days apart and 4-5 days long. What do you think the chances of me being pregnant are? I had my last period around July 16th! I am currently not taking any birth control pills. Please help!