I Can't Drink Now Like I Used to a Few Years Ago (26M), is that Normal?
During college and a few years after (maybe til 23/24) I drank almost weekly and don't get drunk that easily. In terms of beers, maybe I get tipsy at about 6 and give up at 10.
But now, I drink 2 and I get tipsy, and maybe tap out at 4/5.
In general, any kind of sudden changes to your normal functioning are things you should probably be discussing with a physician, even if you're young and otherwise healthy. The really encouraging news is that, if this is indeed caused by a health problem, you're young enough that it's really likely you can completely reverse it and get back to 100%. And if it's not, then no harm done by seeing a doctor and confirming that ¯\_(ツ)_/¯
(Also, not to scare you, but no I wouldn't expect to see that dramatic a decrease in alcohol tolerance over the course of just a couple of years at your age. I think it's worth talking to a doctor about this.)