Stress of the change of homes could be a factor. He is also probably beginning to teeth and ears can drop during that time and then come back up.
As for diet, Toby's breeder's recommendation would be my suggestion to follow. There are many threads on diet, nutrition, recommended foods which have all led to highly spirited debates. IF you are interested in that topic, a search of the archives will give more reading than you might want to do right now.
Welcome to the board!
Debbie