he might be allergic to his food. all commercial/conventional grocery store dog foods are loaded with fillers including wheat and corn that many dogs are allergic to.
please go to a 'real' pet store (not petco) and talk to them about your dog's issues and needs. the higher quality food will be SO much better for his overall health. in addition, if his allergies persist, you may have to put him on a more hypoallergenic diet (like duck and rice).
our pug came to us with some pretty bad fur/skin issues, as well as a raging ear infection, which can all stem from inadequate nutrition. he was eating conventional grocery store brand dog food and treats up until he joined our family. we put him on high quality kibble (natural balance) as well as raw food (nature's variety) and his coat is now beautiful, and his ears no longer are a problem. i do occasionally give him about a 1/2 tsp of coconut oil, as well as a green algae/vegetable supplement, some fresh fruit (apple, blueberries) and sometimes even a scoop of plain yogurt. he LOVES it.
also, watch the treats that you give him, many of them are basically junk food for dogs.
eta: many high end dog nutrition retailers will give you free samples to try before you have to buy a big bag. our dog eats just about anything so we do rotate his food so he gets different tastes and protein sources (chicken, lamb, beef etc.), but if you little guy is finicky you might be able to try some different brands/flavors to see what he might like.