It's normal ..Because you're just 17,..A virgin too
but I recommend that do not masturbate while watching porn ...At least until you're have an experience a sexual intercourse with other man/woman
because you see, it's true that the most important thing organ of sex is the brain ....When you're watching porn movies ....Your brain get a stimulation from the sound and moving picture, so it'll make your body think that you're having sex, and believe me...Watching porn movies makes you hornier more than watching a stripers ...
That's why u cum so fast :lol:
when u get older you'll be wiser, you will use masturbation as a "facility" of practice ....