Ah, well, your original doctor, the general practitioner, knows about as much regarding your penis as you do about deep sea biology. Going to the urologist, as unexpected as that might be, is really the solution.
Any prostate infection is difficult to treat because the prostate tissue is very dense and does not get much blood flow. They can persist and resist treatment for weeks and even months as a result. Don't assume that one course of treatment is sufficient. When dealing with a suspected infection you must continue treatment without a break in the middle, or the bacteria that survive will be the toughest and hardest to kill, meaning that during the interval where you have not been fully cured, the bacteria that are replicating are the ones most challenging to get rid of. Call your urologist immediately and talk about the situation. He may decide to extend your antibiotic treatment for several more weeks. Do not delay.
Peyronie's is unusual in young people. It's fairly unusual in general. And at your age, the doctor is more likely to suspect some vigorous masturbation is or did cause some irritation that is occasionally triggering some pain as a tiny injury gets triggered when you move something the wrong way. Like a little hitch in your shoulder from moving something wrong, everything is fine until you move it just the wrong way and then you get a shooting pain.
I'm not saying the urologist is wrong and that you don't have an infection. It's unlikely he'll know exactly what the source is, even after investigating, unless its very obvious.
Riding a bicycle regularly, doing strenuous exercise, not drinking enough water, lots of things can contribute to tiny injuries in your urogenital system that can feel like a stabbing pain when they get irritated by another activity.
Of course no pain is "normal" and it's good that you're willing to figure out what's wrong. What I'm trying to encourage you to do is to pursue a resolution without any "wait and see" breaks. Because in some circumstances waiting makes the situation worse and harder to resolve, I don't want you to fall into that mode of inactivity where you create more of a problem by not following up promptly. Phone calls to your urologist are free. When you have limited results or aren't fully better, get on the phone and keep him engaged.