Why can’t I get drunk despite barely ever drinking?

It definitely can’t be a tolerance thing. During my late teens and early 20’s I drank fairly often (never to the point of being an alcoholic, but I’d go out for drinks with friends most weekends).. back then I could get drunk with ease.

These days, I very rarely drink. We’re talking maybe 4 or 5 times per year at most, only ever on special occasions. I’m the same height as I was back when I used to be able to get drunk, and I’m only 10 kilos more than I used to be in terms of weight, so it’s not like I’ve grown or gained a bunch of weight, so surely that can’t have increased my tolerance.. yet on the rare occasion when I do decide to go out for drinks these days, I can’t get drunk at all.. to the extent where after 5 or 6 drinks I’ll feel practically entirely sober. I had “too much to drink” on new years, over half a bottle of rum, and AT MOST I felt maybe very slightly tipsy.. in the past if I’d drank over half a bottle of rum I’d probably be throwing up and falling over.

I cannot fathom why alcohol doesn’t appear to work for me anymore, especially considering I barely even drink anymore.. is anyone else in the same boat? Is there any logical reason why this could be the case for me? any potential medical reason? I’m on medication however I’ve been on it for years and I never had any issues getting drunk in the past when I was on the same meds.

If anyone could shed some light on how any of this could make sense, then that would be much appreciated. Thanks.