Some women just have really irregular periods. How long were you on birth control? Sometimes it takes several months for them to fully take effect and sometimes you have to try different kinds to find one that works for you.
However, you don't really want that now, since you are trying to get pregnant. I would recommend getting an ovulation test kit and use that to know what the best time is to try to conceive. Don't get discouraged if it takes a while. It isn't unusual for it to take a year of trying before conceiving. Doctor's don't consider a couple infertile until it's been 18 months.
If it's been that long, you may want to get everything checked out with a gynecologist or go to a fertility specialist. Also, do some research about raising your chances of conception, such as having your husband wear boxers, not having sex too much (it depletes his sperm count), keeping your stress down, etc. Good luck.