He could have bruised his beak scratching his head on the bars of his cage trying to relieve his itchiness. Bruises are hard to see on dark beaks but can be there and take a long time to heal (like a bruise on our nail, it has to actually grow out before it's gone). This past fall, I was at the vet with one of my birds for the same type of injury. He had stopped eating his hard foods and was losing weight. My vet took blood to rule out anything more serious (he was fine, thank goodness) and sent him home with antibiotics and something for pain, which helped a lot. I gave him lots of alternative soft foods and soaked his pellets in juice (remove after just an hour if you do that because bacteria can grow fast in that combo). I gave my bird lots of warm, nutritious birdy bread during his recovery, which helped with his hard molt, too. It was a couple of months before his bruise healed and he regained the weight he lost. Good luck to you and your Grey. I hope he will be feeling himself soon.
