My pewter was being a little finiky when I got him. I put a African Rat in his cage and it broke his habit really quick.
Since you introduced him to your female, that could have put him on breeding alert. My ghost still is deciding not to eat and he hasn't at for over a month. They do drop mad weight when they intend to breed. I have separted my ghost on and off and he doesn't want to eat. Its normal for the season, especially since hes breeding.