Could I be pregnant

I had sex August 31st and the 1st without a condom but we checked for precum before he went inside of me, he also didnt cum inside of me. But pre cum may have got in me. I also had sex on the 12th and 13th of Septiember using a condom. My period was suppose to come on the 18th of this month but it hasn't came yet. Could I possibly be pregnant?