Help!

I went off the pill 2 months ago. My periods have always been regular and normally 28-29 days. My first cycle after the pill was 34 days now I am waiting for period #2 after the pill and going on day 40!!! I have taken pregnancy tests and they are all negative. I am getting very worried that I am not getting my period. I have been feeling offa stomach aches/nausea/etc but got a BFN last night! What should I do? Should I be concerned? Anyone else going through this? Any advice or help would be very much appreciated!!