look, I'm sure you have heard that a lot but you are 16, there is not one girl on this planet who is not self-conscious at 16 :)
As for your weight and size and all, I really don't think that you are fat. You're not one of these skinny sticks either but I would consider this a good thing :)
Also you have to consider that you are in the period of life where your body is undergoing a lot of changes... just let it be... from the moment you are healthy dont' worry about dieting etc.... just eat healthy and live your life! (ok avoid staying home 24/7 in front of the tv )
And... Do not take diet pills. I won't even talk about health problems I will just tell you this: they're very expensive and they don't work. And if they do work, the moment you stop you get back the weight really fast and you tend to gain more than you had previously lost.
Stress can definitely be the cause of weight gain... and that unfortunately is very hard to cope with... maybe talk to your mom about how you feel and what are the reasons for it...
But again don't worry too much, you're 16 and for many people this is probably the worst age to be at.... trust me I know what I'm talking about... :)
Just let time pass, and try to enjoy yourself :)