I am fourteen and started my period when I was tweve. For the first months it was normal and never late but now it hasn't come in like five moths.I have never had sex so I know that I'm not pregnet.What is wrong with me?

Probably nothing... it is not uncommon to have irregular cycles in the first few years of having your period. Some people will be regular right from the start, others will not.
Certainly see about having an appointment to speak with your doctor if you are worried.