Hi there. Yes, periods can be quite irregular in those early teen years. However, 4 months is a bit of a long time. Are you sexually active?
Well I know when I was around that age my period was NEVER normal and sometimes it does skip months especially because your body is still getting used to it. Also, I had a friend who began smoking pot and she consistently smoked for about 2 or 3 months and never got her period. After about 4 months from the time she began smoking she got her period and it was super heavy. I don't know if you smoke or not but those are my only experiences with periods that late.