i feel sad and worried

Im trying to lose weight i have been drinking lost of water everyday i finsh a bottle and i go get another one but my mom and my friends say that i look good for my weight and ik but one time i went to the doctors i weight alot more that what i usally weigh . I weighed 137 and ever since i started school I realized that i ws loosing so weight and now I weigh 125 . My goal is to weight 105-115 pounds but idk what to do does anyone have advice