It is easy to blame a surgery for overfeeding. If a dog scoots on his rear, he has worms. Fleas or allergies are usual causes of the itch. A hot dry nose means a fever. A rectal temperature over 102.F may mean a fever, but that is the only accurate measure.
Dogs eat grass when they are sick.
Dogs are scavengers by nature, and normally will eat all kinds of stuff. Some dogs just like grass, and eat it all the time. A dog's mouth is cleaner than a human's. The bacteria in dogs' mouths are responsible for all that nasty tartar on their teeth, and the bad breath that comes with it. When they are infected, they shed the parasite in their feces for a short time, then they do not shed it anymore.