I believe your doctors concern with having you on morphine, (I take ms contin extended release) is that starting you on that strong a pain med while you are 17, and if it turns out to be a chronic pain problem, by giving you morphine, althought by far not the strongest med available, it may be they would rather try other meds to see if they work before starting you on something like morphine at your age.
I dont know if that is your doctors thinking, but you can ask.
Kathy