Why can’t I stomach shots out of the blue?

I am a freshman in university, living in Canada, and I have always been someone who takes shots at parties/family gatherings. This is due to the fact that I have a very high tolerance and would rather just get it over with instead of having to continuously taste drinks after drinks. Drinks can get easily filling. I am still very young, which is why this sudden change in holding my alcohol is confusing me.

Up until 3/4 months ago I was fine, but now even if I want to drink or pregame for parties I can’t stomach it. I immediately gag terribly and can’t get past two shots.

Google is not helping me out and I have not changed significantly in my lifestyle or body or even the pattern of my drinking (only would do so at big social events) so I can’t seem to understand why.

Has this happened to anyone out of the blue as well?