Can Sex Trigger Periods?

I'm 24, 165cm, 49kgs, and have no history of any medical problems and am not taking any medication, prescription, over-the-counter, or otherwise. I think sex is triggering my periods. A few weeks ago, I had sex with my partner and my period started about a week earlier than it should have. I had sex recently again and again, I got my period 3 weeks before I should have (the time between this and my last period was only 10 days!) So, can sex really trigger periods?