Have you been checked for PCOS/insulin resistance? I was overweight a few years ago and my pds got really screwed up and eventually stopped altogether. Turned out that was the reason, and for two months in early 2002 I took Metformin. That second month I got pregnant.
I went off the meds when I found out I was pg. The year after my daughter was born I decided to get healthy. When I lost the weight, my pds came back and have been regular ever since.
(Metformin can really help with weight loss, but I chose not to take it for that purpose. YMMV.)