Why doesn't alcohol seem to affect me?

First thing that affects tolerance is genetics. It is also what you were drinking. My best friend is about your size, maybe even smaller and made it to 21 shots in 2 hours on her 21st without getting real sick (Not recommended of course). The jello shots have less than a half oz of alcohol usually and the mixed shots that you only had half of also have less alcohol than taking shots from a bottle.