Can Penis Size Be Increased?

I am twenty four years old man.from five or six years old I masturbate.those days I regular masturbate.About fifteen or sixteen I regular done it. Then I try to lower it.And now days I do it three or four days once. ninety five percent I do it just one time.I think my sperm is poor much.they r not enough dense & they r lower in measurement.I never sex.my penis still hard when I masturbate or in any sexual condition. my penis size is four inch.Can I increase it?What should I do for better health & sperm?