Change in alcohol tolerance

Hello everyone I’m currently 17 and have been drinking for about a year or so at house parties etc And I’ve experienced a change In alcohol tolerance where I used to be able to finish a 12 pack of 5% beer and then go onto vodka after that. Now I would struggle to finish a 12 pack to be honest even when hydrated and full stomach Obviously drinking this much is bad and I don’t need a lecture on this Also living in Uk there is a big drinking culture so drinking at 17 is not strange Just curious what could cause this maybe my body is just telling me to slow down abit

Abit annoying as I’ve made a name for myself as a heavyweight and struggling to live up to it nowadays

More info I’m 6,3 85kg

Any advice appreciated