Originally Posted by Allyallyally

My cycle is more or less regular. Around every 26-28 days. I always seem to be a day or so early than I've planned.

I find that sex (or perhaps, orgasms) can sometimes bring on a period slightly early. If I'm starting to feel like it's that time of the month (sensitive boobs, irritable, etc), I've noticed that if I have a few strong orgasms within a day or two, I get my period. If I don't, it seems to hold off for a couple of more days.

And yes, I've actually experimented with this. Several times.