What's up with my Period???

Last May I had a baby, since then I may have had 4-5 periods..

My periods have always been like clock work, since this last time around they have been super inconsistent or not at all. I havent had sex, there's no possible way for me to be pregnant, I dont take birth control I never have, and I'm over a week late yet again. What in the world is going on with my body? I dont have PCOS, I'm 26 (so chances for the whole menopause thing is slim)... Anyone have any idea?