What Causes Shrinking And Thinning Of Penis?

sir, i am 25 years old man height 5' 7"" and weight 62 kg from kolkata , having problem about penis,my penis getting shrink and thinner for last 3 yrs .Now i am too much worried about my sex life in future and also depressed for this problem and its making my life hell day by day.i had an accident in 10 th stasndard when i am 16+ ;i had to cut my left scrotum because of damage and this decision had taken by a doctor. In addition when i am in teenage had many time musterbation and now have this think once or twice in a week-is these are cause of my penis getting shrink and also i have fear that i will became dad or not?? please help me . i am waiting for your help doctor.........send feedback ASP. Thanks i advance