Why can’t I drink like I used to?

Hi, I’m a 25yo male and have been drinking since the day I turned 21. I’ve always since I started been a heavy drinker, I used to do shots, and also four loco for a while, primarily shots tho even did shots of ever-clear to ease a toothache.

What I’ve noticed in the last year is my body is getting fucked up on less and less alcohol (my number of shots I can take decreased) and even now I’m seeing myself wake up and puke after only having 2 12oz beers the night prior, but then other nights I can drink 2 tallboys (this is about my limit if I don’t want to be too hung over the next morning, but I used to drink this all the time and more without issue)

Probably for the best tbh since everyone I know has been worried about my drinking but I’m just curious as to the why this may be happening.