I only have a period every second month or so. I don't feel sick, but a friend said that it could cause problems when I want to have children one day. What is causing this and should I be worried?
You haven't mentioned your age, but it would seem from your letter that you are young. When girls start menstruating, their periods are often irregular. But eventually this does settle down into a monthly cycle.
Your menstrual cycle can be affected by stress, weight loss, unhealthy eating habits and infection. If your periods where regular before, then see a doctor.