I need help!

Okay ladies, I'm confused beyond belief. I've always had a pretty regular 28 day cycle, 4-5 day period length. Last month, my period came on time, but was only 2 days & very, very light. Now this month, I'm 4 days late. I have some back pain, but no significant cramping. I'm so confused as to what's going on with my body. Advice? Aaannnd Gooooo!