What Causes Delayed And Short Periods After Taking LoSeasonique?

I am a sexually active 18 year-old who has been taking the birth control LoSeasonique for around a year now. This current week, starting on Sunday, was supposed to be my period week (which happens at the end of every 3-month pack of pills). I didn't start bleeding and cramping until Tuesday night and it only lasted around a day. I know that the period Seasonique users usually experience lasts around 2 or 3 days, so now I'm afraid I could be pregnant.