This happened to my friend when she first got it. As long as you are not sexually active, then you know that your case is like hers. It was nothing. Also, if you are a rigorous athlete like a runner, this could be a cause.
When you first start your periods it can take a while to regulate, years even. If there's no chance of pregnancy that this is just your body getting used to having periods.
If you're concerned you can always talk to your doctor, but this is normal for someone just starting their periods.