Growth and size

hey Im a 15 year old african american male and I'll be 16 in like 2 weeks......I'm pretty sure I have started puberty cause I have armpit hair and pubic hair also my voice is pretty deep....I use to be really short about a year ago roughly about 5'0 and now Im about 5'4 -5'5 everything seems to growing pretty good I guess but the only thing that doesn't is my penis ....its about 3 inches when relaxed and erect its about 5 ....I was wondering if this condition that I developed a several years ago has anything to do with ...... the condition that I have is that when I urinate ...it burns like crazy ...I've been to a few docs over the past years and most cant find anything wrong and a few say I have a bacterial infection and my step dad says his nephew had the same problem and he found out his urethra tube was twisted and he had to get surgery ......but I wanted to know if that had anything to do with the growth and size of my penis or am i just slowly developing and I also still have a little extra foreskin ......Please help