Sometimes women on the pill have light, irregular periods for several months after getting off the hormones. I didn't even have one for 4 months after stopping the pill. After your ovaries have been shut down for months to years, it can take a while for things to get back to normal. Unless you are trying to conceive, I wouldn't worry about it too much, and enjoy not having to deal with the heavy flow. :-)
I'm not sure how old you are. However, if you the age of 27-40, you could be pre-menopausal or preri-menapousal..hope this helps...