Puking after one shot

I use to drink alot, a couple shots on a empty stomach every night, never had a issue, but the last two times i drank i threw up and felt like shit for two days after. I ate before and mixed my shot half with lemonade and half vodka and puked after drinking it. Did i fuck up my tolerance or something? stupid question but im confused because i cant even keep down half a shot. I cant even sip on it without gaging.