What Causes Irregular Menstrual Bleeding?

Last month I had periode cramps and pains for about a week before I was supposed to come on. I then came on, but it seemed difficult for the bleeding to really break through and be as heavy as normal and it only lasted a day or two. This month, I had no abnormal discomfort before coming on, I was 4 days early, the bleeding was heavier, but again it has lasted for 2 days and now the bleeding is very pale. I've been feeling a bit blooted for a long time. Haven't had intercourse for maybe 5 months now. I'm in my midt forties.