hi...
just to let you know, most foods at the stores are not quality foods.. some do carry Oxbow and Mazuri, they are quality.
the other thing, if you have a food that has all those treats in them, he will eat the treats first, then will not want the food... actually i woudl pick mcdonalds over something healthy myself every day of the week.. but , i'm alreay too fat.
the treats he is eating.. if its not treats in the food, how many treats are you giving him per day.
its not good to keep changing foods... he is eating hay you say which is good. i had a very hard time getting two my guys to eat good on a pellet they liked, and still one of them, just doesn't eat that great... there is nothing wrong with him, he is a fussy little buger that scares me, but i have had him to the vets more than once.. i do not know if that is normal in chins, i haven't had enough of them..
so can you just tell us what you are feeding, how mnay treats, etc.. oh and this is a new behavior, i'm thinking it isn't because you said you have switched foods many times.