Why does alcohol make my stomach hurt?

I recently turned 21 and have been very slowly attempting to get used to alcohol (I didn’t drink underage because I never really felt like it) and I’ve noticed that any time I drink any alcohol at all it gives me a bad stomach ache. I could have one beer, or one shot of whiskey, or half a glass of wine, and every time I feel unwell. I have yet to have anything enough to make me feel drunk and I don’t drink often at all. Am I just not used to alcohol yet and I’ll grow accustomed to it with time? I don’t really get nausea or anything else like that, just the stomachache itself that usually lasts until the next morning. I don’t think it’s a hangover because I feel the pain within an hour after drinking, and again it’s never that much. What’s my problem? Do I just avoid alcohol forever?

I don’t have IBS or any other condition like that (to my knowledge).