What Causes Delay In Periods For Months?

Hi. I was wondering if you could help? I am worried that I might have a disase of some kind. I haven't had my piriod Febuary, and it is now the end of July. I am not pregnent; I am a virgin and have had no physical contact. In August of 2009 I got the 1st Gardisal shot, but did not follow through with the others. What is wrong with me??? I want to be able to have children some day, and am afraid that this will mess it up.
PLEASE HELP!!!
TeYowna- Age: 18- Gender: Female- No cronic illnesses