Talk to Internal Medicine on Weight Gain And Stomach

I want weight gain because I m underweight according to BMI calculations 10 kg I m 8 years old I face typhoid and 14 years old doing masturbate. Now I take healthy diet plan daily but I face some problem for example digestion process sometimes chest inside burn and nocturnal ejaculation more than 2 times in week also I have a asthma problem and face a lot of weakness in bones also face headaches. Now I don't understand where I want to go for check up.