13 and penis is still the same size as it was when I was 12? Worried now

I am 13 at the moment, and i began going through puberty when i was 12 as i began to grow pubes and my voice started cracking, however my penis size has stayed the same since i was 12 and my pubes amount has stayed the same too, (I began growing pubes in January of 2012 and I turned 13 in january of this year) and i have just stared growing arm pit hair but my penis size hasnt increased at all. And now Im getting worried. I know people say you start puberty at different rates but I started puberty like a year ago but its like it has stopped down below like my penis and pubes and started on the above like on my voice and arm pits. What is going on?