allergic to alcohol or intolerant?

I drank a lot from about 15 years old to 25 years old and would get hungover but also be able to deal with it. I used to get blotchy skin occasionally when I’d drink, all over my body. At about 25 or 26 years old, my tolerance went from 3 drinks to hungover to 2 to 1. Now, at 38 years old, if I drink 1 drink I am almost certainly going to be hungover for an entire day and it’s possible for it to carry over to the 2nd day. This sounds crazy but it’s actually how I’ll feel. It doesn’t matter what kind of alcohol it is either. I’ve gotten some concussions from extreme sports, could that have anything to do with it?