[¯|_(ツ)_|¯]

Don't feel ashamed or anything like that about your size. You're perfect just the way you are!

Since your penis is rapidly growing and you are concerned, are you able to get to a doctor to make sure everything is normal and that your hormones are all right? It's better to get checked and find out there isn't actually a problem than to figure out too late that there IS one.

I'm not sure about hiding it since I do not own a penis myself, but maybe it involves how you position your penis in your pants, the direction you point things, etc?

Don't worry about being with a girl. Sexually, if things hurt you can try different positions, moves, and speed until you two get into a good rhythm and things stop hurting.

Masturbation is normal, especially when hormones are raging. The one thing to question is how it is impacting your life. Are you getting hurt at all by masturbating, or is masturbation something that is taking over too much of your time (such as giving up other obligations to masturbate)? If so, that's when it becomes a problem. Maybe you can do something like install a child block on your computer if you look up porn to masturbate to. Even though you know the password it would be a reminder to maybe do something else. Try other activities to distract yourself, such as exercise, video games, etc, to release some of the tension.

I wish you the best of luck!

Dez