it could be nerves or stress. the more you worry about things, often less chance of them happening. do you actually orgasm?
it could be a blocked sperm duct which i had some years ago but was quickly sorted with a visit to a doctor and a course of antibiotics. is your penis hard when masturbating throughout?
if in any doubt see a doctor.
Yes it is hard throughout. How am i suppose to tell my parents. "hey i cant cum so can you take me to the doctor" I am really concerned about this. at first i figured hey maybe i just need more time. but now i am done waiting.
I can definitely see why you wouldn't want to discuss this with your parents. So you could tell them you have an issue with a testicle; that'll get them to get you an appointment pronto. You're over 6 feet tall, so it sure doesn't sound like you're just late to puberty. Not to get too weird, but it does sometimes take some effort; a pretty frenzied pumping of the penis, and it can take a few minutes. You might want get some lube and give it a good five minutes to be sure. Check jackinworld.com for info on masturbation ideas (it's not a porn site).