My name is XXXXX XXXXX X have been a Vet tech for 30+ years. It is so great of you to take Bugs back in and that you are trying to help him. It sounds like Bugs may have overdone the eggs and other foods you gave him. The eggs, especially the whites can be very gassy in a dogs stomach. It would be better to feed a good high quality puppy food diet or A/D dog food or Royal Canin which are recovery foods. You can add some green beans, cooked eggs(yolks and whites) and some rice into the mixture of dog food. I suggest feeding several small meals than one big one. Over feeding human foods is not as beneficial as feeing several smaller meals of a good quality dog foods. For the stomach issues you can give (1) 10mg Pepcid AC every 12 hours, which should help stop the stomach noises and settle the stomach. As far as the Diatomaceous earth it is non toxic and would have not caused the stomach issues. I recommend it for fleas and it has many uses for pets.
I would take a stool sample into the Vet. In the time he was away from you, he may have picked up some parasites that need to be treated in order for him to pick up some weight.
I think you will find a good recovery food will help Bugs put some of the lost weight back on. Please let me know if I can further assist you. I am here to offer you and Bugs 100% Excellent Service. Joan