spotting after period

Okay I'm going to start this off by saying yes I will go take a test. As soon as I get the chance to pick up one I will. Also, my partner and I used a condom. Anyways. My partner and I had sex, the condom came off during sex and we stopped as soon as we realized it, he had not came yet although he typically has a ton of precum.That was a day before my period. My period came but it only lasted three days. My period always lasts seven days. I am 21 so I know my cycles normal patterns. It was heavy but abruptly stopped. Just no blood after the third day. Four days later and I am "spotting" which also never happens to me. Is it possible that I would be pregnant even though I had a three day period? Has anyone else experienced something similar?