Could it happen that a doc. come to know that i masturbate?

Already does: In spite of whatever strange stuff anybody else has told you, essentially all young men and most young women masturbate. It's a good thing unless you're obsessed with erotica and are missing out on work, study & relationships. Guys who use the same tight grip each time get a pigment ring, and this is a common finding. Talk with a sensible grown-up; your doctor or maybe even dad.