My dh has been having strong physical reactions to alcohol for the last couple of years. Until recently, it's been hard to pin down the cause. After one or two drinks, he'll feel fine until the middle of the night or morning and then have a terrible headache, diarrhea, and feel nauseous, sometimes for the entire next day. We thought at first maybe it was from beer, which led us to consider gluten as the culprit. We recently went gluten free, but then a couple of nights ago, he had a small drink made with grain-free alcohol, and had the same reaction as usual. I feel sad for him because he recently got into beer brewing and is a scotch enthusiast, and now it looks like he might not be able to enjoy those things anymore.

I have looked up alcohol allergies, but the symptoms for that seem to be pretty instantaneous, and this is happening several hours later. It isn't the end of the world for him to stop drinking completely. I'm more concerned that this is a symptom of a bigger problem.
We are totally new to food allergies or sensitivities so I don't know what to do from here. Should he see a doctor about this? What kind of doctor? Any ideas as to what could be causing such a violent reaction in an otherwise-healthy guy?