Vodka makes me tired

I’m an alcoholic and have been drinking for ten years or more. I quit for like 90 days but started again a couple weeks ago. I was drinking beer (my usual drink of choice) which was fine but took way too many to get me drunk. I switched to vodka because it was cheaper and to get more drunk, but, I fall asleep now after just 4 vodkas vs. when I drink (light) beer it takes 10+ just to even feel buzzed and I feel far less tired. idk just confused and annoyed as to why this happens. any way to avoid this or get past just being tired all the time?