H.F.
I have always had a very irregular cycle, I ahve gone 3+ months wiht no period and no pregnancy. IN my case it is because of polycyctic ovarian syndrome, a hormonal disorder. It may be that you have some kind of hormonal imbalance. Or if your are breastfeeding it may be that you are not having periods because of that. Ask your doctor for help figuring out what the problem is.