There r valves in the erection process that allow more blood to enter the penis, & hinder it from leaving the penis, & the working of these valves is accomplished through the body using nitrous oxide in the blood stream to work those valves. The brain sends signal through nerves to the penis base area to work this process.
Even though women think that they r way more complex, not so!
Just getting an erection seems so simple, especially at ages of puberty & through most of life, but it is an amazing & complex process.
Then there is the emotional & confidence part as well.
Anxiety from the first problem can even be shutting u down some, focusing on the when it did not work & kind of parking there?
What ur experiencing is so not normal, & it is not genetics, from ur Dad, or u would not even be here! Go to a different doctor who is young, & tell him what happened & what u have gone through.
Ask for referral to a doctor who specializes in males organs & sexual functional.
Do not give up Dude, or accept dead ends, because being 16, u have a really good chance of getting this corrected & no doubt will.
As someone else said, u should be having a difficult time keeping the stone hard erections under control, & explain that to the doctor. Any doctor who is not an idiot should understand that unless he is dumb or lost his total memory from where he was in his teens & 20's
A young doctor in his 20 is will care about ur sex life, relate to ur experience, & want u to have a good sex life. Older doctors r good for lots of things, but not this one.
Wanting the best for u Man, & for us Dudes, our sex is about number one on our list, aside from survival.
Me! :- I