Heather5 is right. If you are trying to get pregnant then I would go see a very good OB/GYN. Even if you aren't trying to get pregnant I would still go see a good OB/GYN to make sure that the missed periods aren't something serious. Myself, I have a period only once or twice a year due to PCOS and my husband and I are ttc our first child. My OB/GYN referred us to a fertility specialist who put me on meds. to force ovulation so just because you aren't regular doesn't mean that you won't ever have a period and can't get pregnant. It just means something else is going on with your body that you need to get checked out. :)
Are you trying to get pregnant? If so, you'd need to see a doctor to get your cycles back on track. Probably progesterone to get your period started and then maybe clomid or some other medication to help you ovulate. (Your doctor will do some test to find out what is appropriate).
If you're not currently trying to get pregnant, then there is still a chance it can happen. Basically, you could technically go months without ovulating and then all of a sudden release an egg again...and you wouldn't know it until 2 weeks after when your period shows up.
Hope that helps.