What Causes Irregular Periods?

I have a 50 ish day cycle and i am trying conceive. I am not sure when i ovualte. I am also concerned as my cycle was 50 days for a couple of years then went to 30 days until Feb 2011. I have previoulsy had 2 abortions and 2 miscarriages (one was at 17weeks severe spina bif & water on brain). I have been leaking from my breast for over 2 years but previous hormone and bloods come back fine. Confused and any advice would help. I have a feeling i may have PCOS but hopefully not.