Welcome to HealthcareMagic. Masturbation
can never cause any damage, reduction in weight or weakness of body. The most common psychological problems can generally be related to: inhibited sexual desire, anxiety
, mental fatigue
, stress, guilt etc. At a younger age people usually have more sex drive and their frequency of masturbation is maximum. You can indulge in this activity as long as it is pleasurable and you have the drive for it. It should not cause you any pain.
Hope it helps you. Regards.