Please help what's wrong with my chicken?

A few weeks ago she was standing still with one eye shut and her mouth open. The next day she couldn't lift her neck and it kept twisting and stuff (wry neck). I took her to the vet and they gave me vitamin E selenium shots and she was completely normal 2 days after the first shot. Now it's happening all over again. I gave her the last shot I had from the vet and she's drinking but she seems so miserable and I don't understand why this keeps happening. Could it be that it's so hot outside? the coop is shaded