Health Question

My 5-year-old boy, Winston has been acting strange ever since we got an addition to our ferret horde last week. At first I thought it was stress, but it's been almost a week and has shown no signs of improvement. He's lethargic, but not having any issues eating, drinking, or pooping. He does do this weird licking thing a lot when there is no food in his mouth, and when he does eat, he twitches his head to the left, down, and back. Any ideas, thoughts, or suggestions are greatly appreciated. I've been trying to research his symptoms but nothing seems to quite match up that I've found.