How old are you? Anyways talking about your problem, i would suggest that excess of everything is bad. Though masturbation
itself is not harmful as such but there are some factors which need to be taken care of:
1. Penis is also an organ and it is very delicate and sensitive too, overuse or manhandling might cause some structural problem, so if you are gentle with it then no problems.
2. Frequent masturbation has two probable reasons, increased sexual desire or getting indulged in porn, both of which needs to be managed because we are not here only to get indulged in sex, we have other motives also, otherwise you may find sexual thoughts ruling your mind always.
3. Another aspect is diet, the semen which is secreted contains high nutrition which is being extracted from your diet, so be regular with your diet having all the regular nutrients like cereals, meat, egg, vegetables, fruits etc. they will replenish the nutrition required.
4. Though impotency is not a usuall finding in cases of masturbation, still if you feel you are having some problem than see a good doctor there your doubts will be solved.
5. You can see a Homoeopathic Doctor also in your city, that will help you considerably.
Wish you a speedy recovery to health