don't worry. men mature at different rates. you just aren't done yet. when you hit 22 and you still have the same problem see a doctor. until then just thank god you don't have to shave everyday.
I wouldn't worry too much. Everyone grows at different rates. My dad says he was 5' 7" in high school and fairly small for his age. By the time he finished college, he had grown to a whopping 6' 5"! I'm not kidding!
And my sister and brother-in-law got married young. He was 18 1/2 and she was 19. She teased that when they first got married he had no chest hair and was fairly skinny. A few years later he had filled out and grew more hair. She just teased that she watched him "grow up" after they were married!
I hope this relieves your mind a little. Like I said, everyone grows at different rates. We tend to have growth spurts where we grow quickly then slow down for awhile. Maybe you're just in the "resting phase" of your growth. I'd give it a few more years and not worry about it too much.
Hope this helps! Take care.
April