I'm also in agreement seeing a picture of your set up will allow us you help you better. Another thing that could be contributing to his food refusal is how are you preparing/offering his food? Are you feeding f/t?

If feeding f/t it helps to make sure the mouse is not only thoroughly thawed but warmed with either a CHE or blowdryer to make the mouse's body hot, especially the face for an attractive heat signature. To give you an idea a mouse/rat's natural body temperature is roughly 100F.

Other potential causes I'm thinking, aside from husbandry is how often are you handling him? Did you give him a proper acclimation period?