Thanks for choosing health care magic for posting your query.
Many youngsters have such kind of feeling before the marriage. Please try to understand that masturbation
is safe and will not cause any problem to you unless you are obsessed by it and doing the act repeatedly at the exclusion of your daily routine. Size of penis is not a concern and your feeling that the erection strength has reduced cannot be validated unless you are not able to have sex with your partner. A valid sex , with out much queries in your mind should not give you any problem.
If the problem stays even after your marriage, then you need to consult a sexologist
or a urologist
for this purpose.
Hope I have answered your query.
I will be more than happy to help you if you need any further clarifications.
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Wish you a good health!