Is it normal to feel the need to masturbate/have sex 3+ times a day?

I'm a 19 year old male, and begining to think I am addicted. I have a girlfriend and she doesn't seem to mind, but even when she's not there i still crave. I also go to the gym 4 times a week and work hard, and don't let it interrupt my daily life, but do we run out? And is it affecting my brain?