Just turned 21, why is my tolerance already at an ungodly level.

I don’t drink much at all but if I go out drinking with my friends, they joke around with me not wanting to drink everyday or a lot, yet when I do drink with them I drink the most and they still pass out on me and I’m babysitting everyone😭. I’m only5’7 and 165lbs so I should’ve been on the floor. Last night is an example, 20shots of 70proof vodka. It’s not safe I know this just curious as to why. I’m not a daily drinker so there’s no way I “built up” a tolerance. Be it I am picky with alcohol, I don’t drink anything with sugar, mainly for my reflux. Sugar no good.