Can anyone please help me to find the reason of delay in menstrual cycle?

I am 19 and I have not had my period from last two months… I have not asked about this to any one as I feel shy in discussing all this to anyone. But I am really worried because I know that it is necessary to have your period every month for a good menstrual cycle. I never had sex so there is no chance of me being pregnant. So I want to know what can cause delay in menstrual cycle. Any help will be great… thanks…