I had unprotected sex. Since then I had two periods the last two month's, at my normal time of the month. But they were heavy but short, with no clots. If I'm pregnant I should b like 3 weeks I think. I have no symptoms. But what could cause my period though be shorten with a little pink blood before it starts and no clots?

You may want to go see an Ob/gyn doctor to discuss and possibly perscribe birth control and make sure your hormones are OK... sometimes stress, activity, and hormonal changes affect period. Did you take a home pregnancy test ?