Why does my tolerance change to higher or lower each time i drink

Nearly every time i drink, i drink the same amount of vodka around 0.3 l or so. However if i drink, im rly into it at times after lower than that and at times i feel only a bit drunk even after slightly more than that. I tried documenting what i ate that day and even after nearly eating the same things on these days there’s a significant change in how alcohol affects me.

tl:dr Why does my tolerance fluctuate even tho i drink the same amount and ate the same things that days.