I'm sixteen and looking to loose weight!!

Hi, I am currently 16 and I weight about 175 lbs. During the last year I have gained about 30 pounds, from which I assume is from stress. I just feel like am unhealthy, and I would really like to get back down to my original weight, or maybe even a bit lower. Also, is stress the real reason or this weight gain? My mother has PCOS and I wonder if this weight gain could be a sign that I too have PCOS. I would just really like to get healthy and figure out why I gained so much in a year. Any tips, diets, or workout schedules I should try?