Why do I suddenly have this happening?

So I’m trying to figure out why over the past year suddenly when I drink I end up completely blacking out and being violent and not even knowing when I hit that limit when just a year and a half ago I was able to drink without any problems? I also developed an allergy to alcohol after my gallbladder being removed and if I take Claritin I don’t react to the certain histamines in most alcohol, but I can’t understand any reasons why I suddenly just disappear after a small amount now? It doesn’t matter what it is, it just happens, and I turn into a horrible person. I can have one or two mixed drinks and a few shots and be fine, but anything passed that or specifically more than three beers or more than 5 shots I just randomly turn into someone else. I don’t feel it coming on, I can’t tell it’s going to happen, I feel fine and it’s just like a switch. Is there a reason why this happens?