Remember this happened to me not last month, but the month prior?! I posted about it in the girly thread. Mine was 5 days early! And really, really bad!
I learned:
If you're on antibiotics, your period can be a bit out of whack. I wasn't on antibiotics.
Certain allergy meds can make your period weird. At that time, I started taking Zyrtec on the regular. I looked up effects from Zyrtec and was shocked to see blogs about how shifty this stuff is for people. So many women reporting their periods being all effed up, deep depression, major anger, etc. I stopped taking immediately.