The first day of my last period is on 29 of August 2013. And I had sexual contact 15 day after my last period. I'm expecting my next period this September 25. Until now it didn't come, is there a possibility that I got pregnant that time? Even if I have an e-regular period? Thanks...

You had sex, so you could be pregnant. There is no way to tell at this point, You have to miss the next period. If you miss that period, you wait 2 more weeks before you do a pregnancy test.
It is a waiting game name