I've had a similar experience with my carpet.
Most likely your feeding him to frequently, even if you don't think you are.
Dont feed him for two weeks..let him get hungry and replenish digestive fluids. By then I'm sure he will be happy to take a mouse. If he doesn't take him to a vet.
Ever since I followed through with these steps, for my carpet. He's been hungry every feeding and hasn't threw up a meal.