Why is my period so irradic?

I haven't had a menstrual period in over a year, after i stopped taking birthcontrol pills that is. But now, a year and 5 moths later, ive been on my period off and on for a month, some days ill bleed and some days i wont. my stomach & back hurts alot right before i begin to bleed again which in turn causes my right leg to cramp really bad. and also i have really bad hot flashes, and they steadily get worse through out the night..thats the only time i have the hot flashes. Why is it doing that?