Irregular to regular?!?!

So last year, I gave up my virginity. It was great but the guy and I didn't work out. After my first time, my irregular periods became more and more regulated. By irregular, I mean periods being 1 day or several weeks long or light flows to a butcher's workshop. I'd either have no cramps or I'd feel like knives were being stabbed into my uterus repetitively, and getting my period about twice a month or not getting it at all. But it's changed since. Now it comes once a month, 6 days, heavy flow. It follows the cycle of the full moon. Any explanation of why this is?