bigandlong: I have had a very similar growth pattern. I am just over 19 years old, and when I was about 15 or so my father took me to the doctor because I was not going through puberty. The doctor checked me out and found that I had problems with my testicles and pituitary gland. At the time I was about 5'1" and not developed at all. They started me on hormones and drugs to help with puberty and I started growing about six months later.
About a year later, I started noticing my growth and measuring and was about 5.5" inches then. Well, I just kept growing at a regular pace and by the time I was 18 I was 5'7" and 9.5" long. When I passed the 10" mark when I was 18, and the twelve inch mark about 9 months later. It was a bit thrilling to think that I was bigger than 99% of the guys around, but it was kinda scary at the same time that I kept growing. I have pretty much gotten used to the size, but am still a bit unnerved by how big it is and that it seems to be still growing.
I am about 13.5" x 8" around now, and have added about a half an inch in the last 3 months. My girlfriend that I had for about 2 years broke up with me about 6 months ago because she said I had gotten too big for her. I had been about 7" or so when we started dating at 16 or so. I think a lot of it was because we are going to separate schools now in different cities, but who knows.
I hope that is stops growing at some point. :-*