i dont think with erectile dysfunction you can get hard at all on your own..im not sure though. your doctors probably right.
Erectile dysfunction at your age would be extremely rare and like your doctor said, it tends to be psychological. Your mind has a lot of power over what happens to your body physically. If you feel nervous at all, upset, stressed out, etc all of this can affect erections and cause you to lose it. There really isn't a quick fix, but it'd be good to try to think about what else may be going on in your life. If you feel stressed out from high school or have mixed feelings about sex, wanting it but also thinking it's dirty and wrong. These are feelings you can work through and get better at. Then make sure to be relaxed and just focus on the act(masturbation or sex) you are doing. Don't put a big amount of pressure on yourself to keep it up or else you will continue to lose you erection. Good luck.