On Friday I took my 2yr shihtzu to the vet because he sick.the vet give him a cough medicine and antibiotic called baytril I am concern because he eating is so poor I got take
Him back to the vet on wed

Try boiling some chicken breast or hamburger and mix in a small amount of rice. Try and hand feed him if he won't eat from the food dish.

Is he drinking?

If his throat is sore from coughing or illness, he may not feel like swallowing anything that might scratch. Mincing boiled chicken and adding the rice might be softer going down and you can modify the texture as he gets better.