I agree with Angebelle on reducing your weight, too much body fat throws off ones hormones. As far as birth control goes, it's really not going to do any good. I'm 5'5" 118-120 lbs and I have never been over weight, but I have PCOS and have hormonal issues and everytime the docs put on my birth control, my hormones got messed up even more. I would get a period every 2-3 months on my own and when I was on birth control pills I would never get a period. So birth control pills don't always fix hormonal issues. Try to eat healty, cut out all the junk foods, like sweets, sodas and fried food and try to excercise 5 days a weeks. Do cardio and wieghts. If you lose weight and still don't get a period, I would check with your doc and have them ran some tests to check your hormones before they put you on anything.
Phephe, thank you for sharing. Without a doubt, your current weight plays a major factor in your menstrual cycle. Body fat produces estrogen, which is an important fertility hormone. However, too much estrogen from excess weight can keep you from ovulating regularly or from ovulating at all. This is most likely what you're experiencing. Too much weight can cause insulin levels to rise, thus triggering testosterone hormone level to rise as well - not a good thing for a women's fertility either.
Birth control doesn't necessarily cause additional weight gain. I say this from experience. In fact, my weight didn't really change over the six years I took it. Same thing with my friends. As far as I'm concerned, gaining weight while on birth control is a myth. So, don't rule out birth control.
Since you are 16, you have a few years to focus on you, reducing your weight, and becoming the healthy individual you want to be prior to marriage and child. Best of luck to you!