Do I need to see a doctor? ?

You are not fat at all, actually you are underweight, a normal weight for women/teens is 100lbs at 5 feet and you add another 10lbs for every inch so a normal weight for you is 180lbs, you need to take care of yourself and eat right, exercise is good but you need fuel(good foods) to keep your body running properly. I think you should see a dr. it is a eating disorder and for your own safety it needs to stop