upset stomach

my dog got his shot 2 weeks ago and a dewormer since he has lost his appitite i took him to the vet on wed 2/25 and they said he might have an infection gave him antibiotics he was eating ok but again today has not eaten one bite his ribcage looks a little bigger than usaul when looking at it from the top hes a greatdane shepard mix 25weeks old

I'd say call the vet office back and ask if they think he needs to be seen again or have his medication changed. Once in a while some meds can upset the tummy.