Sudden alcohol intolerance?

Within the last year I haven’t been able to tolerate alcohol. It came on very suddenly along with other health ailments. I try to drink socially and after half a beer I feel like I am beyond drunk. I get super light headed, really sick to my stomach, dizzy, my heart pounds and I feel so thirsty. The worst part is i flush. Horribly. My face and neck get beat red and super hot. Which makes me feel even more sick. I have a lot of gastro problems but none of them should cause the flushing according to the doctor. Any thoughts?