Why don’t I feel affects of alcohol?

I just turned 21 very recently, and decided to have a Moscow Mule with a few friends for my first ever drink. My friends and I all had the same amount of alcohol. They started feeling a bit drunk, but all I got was a bad headache, and nothing else. I decided to try a twisted tea today to see if maybe it was just the vodka that made me feel like that, but same feeling. No tipsy feeling, no drunk feeling, just an insanely bad headache. Does anybody know what could cause this? I’ve tried to google it, but the only answer I could find is that “People who drink often have a high tolerance.” But those were my first 2 drinks ever.