Cramping but no period?

Gabriela
For the last half of the day I've been feeling an on and off pulsing pain below my belly button.  It's not on one side and I'm only on the 13th day of my cycle.  I haven't had spotting or anything.  I've only had two periods so far and I'm 14, and that cycle lasted 43 days (I'm very irregular). I've also been getting headaches.  What could it be?