I'm 15, and my penis stopped growing?

I know it sounds crazy, but I think it's true. My penis has been really small for a while. It grew at one point to maybe an inch and half in length and maybe 2 inches in girth when I was 13, that's also when I got a little taller and my voice got deeper but since then my penis hasn't grown. People say puberty lasts forever or until you're around 21 but I hardly believe it, why has my penis stopped growing? It's been 2 years and I'm stuck with 4.5 inches and 5 in circumference, while other kid's are still growing by the inch! It really depresses me I know it's how you use it but I just really want a bigger penis. I just developed arm hair and leg hair, growing a little bit of a mustache but not really but still I feel like I'm well into puberty and in fact almost done and my penis is done growing for some reason since it's been over 2 years and I already had my growth spurt at 13, I'm guessing. I really don't want to ask my doctor if my penis will grow as I don't even think he'd know the answer. Does jelqing work, because if it adds an inch or two, then I'm fine with my size I just want to be average. I'm really concerned please help!