Hello and thank you for using this site to help you.
The problem with bones and human food is that bones are considered a non food item (unlike a piece of soft meat) so they have the potential to cause an obstruction of the bowel. This would show vomiting , diarrhea ,sudden lack of appetite (or anything the dog eats or drinks may come back up right away) and lethargy. Because you know he ate a bone it is best to get an x ray to be sure he does not have a blockage. Another problem with bones is that they can splinter. When this happens they can pierce the bowel which sends poison through the body.
When it comes to human food , this can cause pancreatitis which will also cause the symptoms you are seeing. In some cases this requires hospitalization for IV fluids.
I would take the dogs other vital signs as well, look for pale or white gums, do a capillary refill check and take the dogs temperature. I am going to direct you to a site to take you through this and it is a good link to bookmark for the future.
Since this has been going on for a while a hands on exam is recomended.
The only other option is to try a bland diet of boiled white meat chicken (no skin no grease) and cooked white rice after fasting the dog for 24 hours of all food . But I think you are looking at something more serious than stomach upset or a bug of some kind and likely it was the rib bone that is cause the problem.
What is normal in dogs :taking the vital signs http://www.petplace.com/dogs/what-is-normal-in-dogs/page1.aspx
obstruction of the bowel
Danger of bones link here. Even if a dog has eaten bones all their life it just means the owner got lucky, a dog can still have a problem down the line from eating a bone or any non food item.