Hey man,
I was searching the internet for info on Klinefelter's today when I found this thread. I registered to write to you because I feel like I've been in the same position as you are in now. Ever since I was younger, I've had a "different" looking body than all the other guys. I was overweight when I was little, but grew out of it once I got into Junior High. Even then, I still looked different, very similar to how you look. It sucked growing up and having the same body when all of the other guys grew up and developed muscles, abs, etc. Everyone was shallow at the age; good looks/attractiveness was the only thing that mattered.
I know you seem pretty set on your self-diagnosis of Klinefelter's... It would explain so much right? It would give reason to everything, all of your troubles, low self-esteem, etc. The fact of the matter is this: whether you have Klinefelter's or not, this is you man. I know it's hard to feel good about yourself in this world when you feel like you don't match up to society's definition of attractive, believe me, I do. But there are so many more ways to be attractive, successful, popular, etc... You just have to accept yourself for who you are, no matter what. It's certainly not your fault that you were born the way you were... Why spend your life wishing you were different when you could say, "I don't care what others think. They're stupid and shallow and I feel sorry for them."
You seem like a decent person. Try not to get discouraged... If you do have Klinefelter's, try and make the best of it. If not, try and accept that everyone is made differently and being different isn't a bad thing. Society may determine the standards for success and attractiveness, etc. but only we have the final say. I've been active and tried working out before, but was never satisfied with myself until I started focusing on the more important things. I'm 21 now, and going to school to be a doctor (Pre-Med currently). All the guys I know at our college who run, work out, and have great bodies are either idiots who are going nowhere in life, or losers who will never succeed in building a relationship based on anything other than attraction (which won't be good). Junior High/High School = girls looking for the "hot" guys. College and later = girls looking for the smart guys, or guys who know what they're doing with their life. You'll be okay, just hang in there. Get a chromosome (karyotype) analysis if you insist on knowing for sure.