Weight loss on depo provera shot

Patient: I have been on depo provera for a few years now. I have had constant heavy periods without it stopping. I can not seem to gain weight, instead I constantly lose weight. I have been to the doctors multiple times and they refuse to believe that it may be the depo provera, even though it only started happening since I started taking the depo. Is there any way that the shot can cause weight loss instead of weight gain? And how can I stop my periods without having to take a pill every day? Please help my body is going crazy ): oh and if it helps, I am 18 years old,I am five foot ten and weigh 105 pounds when I am supposed to weigh 130, and no matter how hard I try I can not get myself past 115 pounds.