If all your vet has to say is, "Feed the dog", then you might need a different vet. Reasons a dog may not eat his/her food:
-Doesn't like food you are giving.
-You are feeding dry food-only.
-Feeding too much.
-Dog is sick.
-You are feeding too many treats between dog meals.
Sometimes dogs don't like the food you are offering, or get tired of one food. Don't buy a huge bag of just one food in case the dog gets tired of the food. If your dog doesn't like the food you bought, most pet stores will refund your money.
Try a different food, and then mix a little canned food with it and a little water. Most dogs DO NOT like dry food without anything else added. It just doesn't go down well, and doesn't taste very good, either.
Dog food bags usually suggest more food than a dog can eat. Feed less than the bag suggests, as long as the dog is maintaining his or her weight. If you are feeding too much food, the dog just will get tired of eating. Besides that, a dog should not be on a SELF-FEEDING program. Meals should be offered two times per day: once in the morning and once at night. Put the food down and if the dog hasn't eaten in about ten minutes, take it back up.
If you are feeding too many treats between doggie meals, the dog won't be hungry. Stop giving treats and see if that helps.
But, if the dog is sick, it won't want to eat. If your dog is too skinny, or lethargic, or has any other symptoms, it needs to go to a vet who will diagnose what is wrong. If you are giving too much food, then give less food.
Consult with a different vet if your dog continues not eating.