Please don't let this go too far before it's too late.
Due to a lot of intense exercise and rapid weight loss I lost my monththlies for nearly 4 years. Obviously it is very dangerous if your hormones to out of kilter, one of the main problems potentially being loss of bone density thus increasing the risk of developing osteoporosis in later life. This is especially critical if you are still in your teens and your bones are still developing.
There is more info on my Sparkpage but to cut to the chase, at the end of 2011, I started my monthlies again after them being absent for nearly 4 years. It took a lot of nagging from family and friends, a few health scares and intense hospital treatment with a specialist team for me to finally accept a need for a more healthy attitude to exercise and eating.
I'm not for one moment suggesting that you have any of the problems I'm forever battling with, but thought that I would just sound a kind note of caution.