What Causes Delay In Periods, Headaches And Lower Backaches?

I am going to be 46 in august and I have missed my period for april. I have been diagonsised with an ovarian cyst a few years ago and my periods are heavy. I have been having headaches and a lower backache for the last few weeks with cramping on and off. would you know what could be causeing this. I have lost 40 lbs recently and I am 5'7 and 164.