I have been taking Zoloft for about six months now, and for the p...

I have been taking Zoloft for about six months now, and for the past six months I haven't had one menstrual period (this isn't unpleasant, but a little worrisome in its strangeness). I am sixteen years old and I weigh 130 pounds. I take 200 mg of Zoloft (sertraline) every morning for depression. I am constantly in emotional turmoil internally, but I rarely have the motivation to express any of it, which leaves me a bottled-up mess. I have gained about five pounds on Zoloft, and I exercise frequently and watch my diet in an attempt to avoid more gain. My emotions, ideals, thought patterns, and self image are all extremely volatile and they change constantly. If I don't take Zoloft for one day, I feel slightly more energetic and I always have detailed, vivid dreams that night. If I don't take Zoloft for two days, I get a splitting headache, I am aggressive and histrionic, and I feel tense and hopeless. These disturbances are only slightly more unpleasant than how I feel when I take the medication; hence, I usually take it. However, if I gain one more pound while taking this, regardless of withdrawal effects, I will discontinue the Zoloft.