irregular periods

I used to always get my period the first week of the month usually on the 5th. I've been Sexually active with my boyfriend of 2 years and I'm not on any type of birth control but the past 2 months it's been coming on the last week of the month. A few months ago before my period got set back I only had a period for 2-3 days , the first day was heavy and then the second and third was super light and barely showed up on the toilet paper if that helps any! Just worried is all.