Don't stress too much about it. I am having the same trouble too. To think I am only at clomid. Sometimes I miss it like a week and boom AF shows up. I think our systems get confused with all the hormones introduced.
My cycles are always very different too, even when I've had the trigger shot, been on Clomid, etc. I guess our bodies just do whatever they want. It certainly makes it tough on us trying to get preggers though. Stay happy and SSBD!!!