Not gaining weight

I am fifteen years old and weigh 96 pounds. I have not gained weight for two years, but have continued to grow taller, now at 5'3". I am scared there is something wrong. I have tried a couple different diets. Within the last few weeks I have stopped eating all meats except chicken, not related to my weight, I just don't eat it anymore. I ride horses once or twice a week and swimm almost every day, but other then that I am not too active. I have talk to my mother about it, but she doesn't seem worried and always changes the subject. Do you guys have any recommendations? Should I go see my doctor about this? Is there a diet I should try? Or is all this normal?