Hi Mel,
As you've been off BCP for almost 2 years your body would have totally readjusted by now. From what I've heard cycle length variation of up to 5 days can be considered normal. Isn't it just totally typical that the moment you TTC your body decides not to behave! Stress can affect the length of your cycle - perhaps the pressure of TTC has had an impact? Regarding the possibility of endo my sister was diagnosed with endo via a lap (the U/S came up -ve). Try not to stress over things - you could totally be pg and its just too early to tell! You'll find out one way or another very soon I hope. If you're not then wait and see what happens next cycle. If things aren't normal again then perhaps its time to try some further investigations to put your mind at ease.
Wishing you a BFP this month!