How long did it take for your dog to feel better after taking antibiotics?

we took our dog to the vet on wednesday because he was dry heaving and had yellow drainage coming out of his nose. he was given a shot of baytril. then prescribed baytril for a week. it is now the beginning of the fourth day of antibiotics and he is still dry heaving (Not as much) and has some yellow drainage. He ate ok on friday, a bite on saturday, nothing sunday and nothing today. today is basically day three with no food. should he start to be feeling better? how long did it take your dog to start to feel better? day 7 of meds is wed