I got my first period when I was in grade nine in August 2008. I skipped out on my period for the next three months and then I finally got it again when it was December. I assumed that was normal, as I read online many times that people skip the first few months until they get a regular cycle, so I didn't worry too much about the skipping. But now I worry, as it has been a year and 3 months since I had my last period and I am now in grade 10 and am still a virgin, so I am certain I am not pregnant. What is wrong with me?

One thing I have learnt is that every single body is different. There are no exact rules about what our bodies should or shouldn't do. If this is your body's pattern, then there you are.
If however you sense that there is something wrong, tell a doctor who can look at all your specifics and rule out a whole lot of your fears. If you get told that everything is normal, then you have a better idea of your own biology and a closer description of your body.
Worry just wastes time and energy.