Sir, why after masturbation my penis and testes pains?

Technique: If you're excited for a long time beforehand, especially at your age, you're likely to have some venous congestion that produces discomfort especially in your testes. Rough technique can make any part sore -- do you have enough support? Don't list this as a health problem -- it's near-universal in young men and helps you stay comfortable and learn about your changing body. Best wishes.