Why isn't HGH working?

I have been on HGH for 17 months now, and I have seen very little change. I started at 2mg and now I'm at a 5mg injection daily. I am 14, and was 4'5 when I started. I have only grown 2" in 17 months on HGH. I have seen almost no change in my body structure ( fat, muscle, bone). Why isn't it working? Or is it just working very slowly?