HOW DO I REGAIN MY OLD DRINKING CAPACITY

I started drinking around last April in college. And I don’t know whether it was due to my genetics or what, but I could drink like a beast. I could gulp up 300 ml of Rum in one go. Even my friends who had been drinking for years used to be shocked by my drinking ability. However, last September I pushed myself too far and drank around 600 ml of Vodka and Rum and around 2 hours later started puking like crazy and almost choked on my own vomit. Ever since then, I don’t know what happened but I can hardly drink 3 pegs. And even when I do, I start puking. Has my body developed some sort of defense mechanism after that incident. Has anyone else faced similar problems?