Dr i am 21... my weight is 84 i get tired very fast. .. and my stamina is also very low. ... what should i do to become fit soon?

It seem like your: Are looking for specific solution . Testosterone ? I would recommend to have a full history and physical examination . When appropriate to do blood work to find out if you have any treatable. Endocrinological /metabolic disease that explain for your small weight and symptoms . I also consider to do full psychological evaluation to see if any emotional problem is contributing to the sign and symp.

Eat more: Keep track of your calories. You must take in more calories then you burn. There is app for phones called myfitnesspal which can help you keep track of calories. Eat 6 smaller meals a day rather then 2-3 big meals. Have breakfast every morning. For healthy weight avoid fatty foods and try to eat healthy. Keep track of calories in and out. Take multivitamin every morning. Sleep 8hrs a night.