No period

For the past few years, my periods have been extremely irregular. I had cancer and my doctor said that I might become sterile, so when it started happening, I figured that's what it was. But a year after my treatments ended, my periods started again and I got tested to find out if I was fertile - my doc says my ovaries are really cranking out the estrogen and that I could still get pregnant. But it has stopped again - it's been almost 4 months since I've had my period. Weird thing is, I still feel like I'm ovulating, occasionally get cramps and other symptoms like I normally would, I just don't bleed, and I'm not pregnant. But I'm not having menopause symptoms either. It's very confusing.