First of all, what did the vet say (s)he thought was wrong and what pills were given? have the dogs had the entire course? if they are boy dogs and a lady dog is in heat locally, that can put dogs off their food. Have you changed their diet or routine? have you started using one of these new scented washing up liquids, they can leave a scented residue on things, strong enough for a dog to pick up. Has a member of the household left, eg to go to college, have you got any new household members, have you moved house?All basic stuff I know but I hope it helps.