Completely lost tolerance, hangovers are worse, alcohol makes me gag now?

Hi, I’m a 21f, been drinking since I was 15. Last year I was drinking pretty regularly on the weekends, I never experienced hangovers and didn’t even need a chaser with shots. I took abt a 6 month alcohol break and have now been drinking a lot this past month. My tolerance obviously lowered, but I also noticed I can’t take shots anymore without gagging. Literally spat tequila all over my floor one time. My hangovers are terrible now, whereas I didn’t feel any effect from them previously. What could be the cause of this?