early cramps?

im on cd 15 about 10 days before af and im cramping it started last night for about 15 minutes on my left side and it was kinda just a sharp pain then went away and i started cramping today around 1 and havent stopped..... o and when af does come i never cramp i usually only get a big headache and a pimple by my hair line the day before or day of af so cramping is not normal for me.... what could this mean???