menstr. query from pre-student

Hi everyone! I sort of lurk on this board as I'm heading for NNP school soon (67 days!). So I know you guys get a lot of "this is what my period's like, what's wrong??" posts, but this one is more for curiosity's sake. I went off the pill after my last period (yes, using condoms since) and my period this month was a)five days early b)short and heavy (3 days instead of the usual 6). Pretty wicked cramps, but absolutely not a sign of PMS, which I normally get badly. Figured this was normal given that I was coming off BCPs. It ended yesterday morning, and then last night, when I would have started with the PMS in a normal month (regular cycles were grand) THEN I got the bad moodiness, weight gain, etc. that I'm used to. Cramps and back pain again today. It's like I had my period backward. Anyway, I just thought it was kind of strange, wondered if anyone had any thoughts on the subject. Probably just my hormones out of whack, took a negative HPT. Anyone encountered this?

Thanks for reading!