Hello dear,
First of all remove all myths & misconceptions from your mind about
masturbation.
In fact, Masturbation is completely normal & doesn't have any bad effect to the body and mind unless you get addicted to it.
Regarding the problems of
underweight &
tiredness, you need to get certain investigations like
complete blood count, thyroid profile, estimation of blood sugar level to rule out any chronic infection,
hormonal and metabolic causes for the symptoms.
Moreover, you should not compromise on regular exercise & routine healthy food such as:
1. Consume more of natural diet like fresh fruits, green vegetables, milk, eggs, wheat, etc.
2. Avoid oily and junk food.
3. Stay away from smoking & alcohol.
Take care.