Jess, I agree with LoveMaltese's advice. What has happened is, when you change a dog's diet AT ALL, even if it's just a diff kind of same brand food, you have to introduce it slowly, by, for example, mixing 1/4 of the new stuff mixed with the old stuff for a couple days, again for a couple more, until the change is complete.
The lamb bones MIGHT make things clog up, and explains the yelp your dog gave out when you touched his tummy...