Why has my tolerance gotten lower?

19, afab, around 53 kgs Like the title says, I have no idea why but my tolerance has gotten worse over the past 2 years or so. Used to get tipsy after 2 beers, now i take a couple of sips and start feeling sleepy. I don’t take any new medication, I’ve Lost around 3 kgs, no other changes. Anyone knows what this could be caused by? And if I have to worry about it?