No I'm not sure. I think about 17 or so days PO. And while on BC my cycle averaged 28-29 days. Off of BC my cycle is anywhere from every couple of months to 1-2 times a year. The doctor and I were hoping that a year of BC would help regulate me to start trying again.
While on BC your cycles are going to be very regular because your body is being given hormones and then removes the hormones for the "period", which is actually a withdrawal bleed. I've discovered with all my research, and my own personal experience, that many times when a doctor prescribes BC to "regulate" a persons cycle it does not actually do that and you can often return to where you were at before. This isn't always true, but it's true for a lot of women.
Did your doctor figure out why your cycles were irregular? Tests or anything? I found that using Vitex was a great way to regulate my cycle. I went from 40 day cycles to 27 day cycles.
Typically the main part of your cycle that will (usually) stay the same every cycle is the luteal phase. While your O date can change drastically your LP stays approximately the same (typically 12-16 days, depending on the person). If you are 17 DPO then I would think that you might have a good chance at that BFP! Do you temp? As long as your temps are still high, you have a good chance there was conception.