Period change. Should I be worried?

Im 17 and In the beginning, my period was definitely inconsistent. I would have months in between each period. Once I lost my virginity and was having sex, my period started to regulate? And it always lasted for 7 days. Which is nothing new. Now it's been a little over a month since I had sex, and this period only lasted 3 days! May seem normal to some, but to someone who usually has a period for 7 days I'm little worried. Should I be? Is something wrong?