Irregular bleeding and cramps?!?!

Little bit long but really need advice.. my period is always on time, never a day late or early and last month I had it normal then 2 and a half weeks later I was bleeding heavy for a few days, since then I have had extremely bad cramps where I've not been able to move because of. Anyway, when my period was originally meant to be due it was a week late and only lasted a day and i got spotting 4 days after? After that the pain completely stopped. Has this happened to anyone else and why? Sorry if it's tmi but any advice or feedback would be really appreciated x