First, let me reassure you that this is hardly unnatural, or uncommon. At 17 years old, your hormones are in full swing, and feeling the urge to masturbate more is part of that.
I'm guessing that now, you're finding the ladies around you at school have been developing nicely recently, and that triggered a subconscious desire to satisfy yourself. In other words, you're seeing more and bigger breasts, which makes you want to masturbate.
And this kind of thing isn't limited to just seeing boobs. Your mind is probably seeing sexual stuff wherever you turn, and your penis is responding instinctually.
I guess the point I'm trying to drive at, here, is that you shouldn't get too worried about the frequency of your masturbation. It's not unheard of for a 15-18 year-old boy to masturbate more than once per day, after all. Unless you're masturbating so much that you literally can't focus on other things you enjoy, just relax.
Oh, and regarding your concern towards the whether or not masturbation can upset your physical health, I don't see any reason to worry about that, either. Masturbation, and more precisely, orgasms, is so natural that your body welcomes it. Endorphins, and all that.