Something i forgot to ask, are you taking any prescribed or over the counter meds? sometimes they can mess with your cycles, and you should check with your doctor to make sure which ones could be doing it.
Another thing to think about is your stress level. THAT can REALLY mess you up.
Hello
I am writing to say that I have had the same problem. i dont know if you are on birth control or not, but i am on YAZ, to control my PMDD. Last year i missed 2 months of my cycle, and i had just done it again in the past two months. The funny part is, i had a 3 week cycle in May, and then nothing. I just finally gotten a full "normal" cycle, which i am not complaining, because i needed it, even though its been hell. Anyways, my point is, I talked to my OBGYN about it, and she said that it can happen, but when you go 3 months with out a cycle, you need to get your self in and checked out.