I'm 19 Years Old, And My Penis Is 4 Inches

I'm 19 years old, and my penis is 4 inches when erect, I haven't grown anything since I was 15 years old. It been the same size for 6 years. What's going on with that? I'm always getting these erections like a 13 year old. My scrotum is 3 inches wide. I have facial hair and everything. I am circumcised, as well. Is this normal? I'm very worried. I am not sexually active. I am 6'4, 200llbs. If I want my penis checked by my doctor, what do I ask? Say? Tell the receptionist? Or just ask for a complete physical?