What specific kinds of shampoos has he been bathed with?
Any medicated shampoos?
Does he skin feel a little greasy?
Are his ears clean, any odor to them?
Yeast is one type of organism that will grow on the skin. It can smell worse shortly after a bath because the moisture from the bath and the warmth of the dogs skin can increase the growth of the yeast. Antibacterial shampoos usually will not treat yeast infections.
Most skin yeast infections have a fruity, musty odor. Does this seem familiar?
You may need to use an antifungal shampoo on him. Miconazole is commonly used on dogs for skin yeast infections. I use one called malaseb. You can usually obtain them from your veterinarian. Some forms are available at pet shops. Chlorhexaderm used in a higher concentration than the antibacterial strength can be used to treat some skin yeast infections.
Do you think this could be your dog's problem?
If you have any other questions please let me know.
If he does not have an active bacterial infection on his skin he does not need to take an antibiotic. Some times when dogs have a bad enough yeast infection they will itch and dig a lot. This can lead to a bacterial infection. And sometimes it can go the other way. A bacterial infection will damage the skin and allow the yeast to get a foot hold.
If all you are seeing is dry skin and a little scabbing then you are probably fine to just use the shampoo. If his skin would become red or you notice a lot of little bumps this can be the start of a bacterial infection.
That is the first place to start. Bathe him with the antifungal shampoo every 3 days for 3-4 treatments. If he does not seem greatly improved then I would recommend taking him to your veterinarian and having them assess if he would benefit from a course of antibiotics.
If his skin would break out again in red bumps or he would start digging aggressively at himself then I would get an appointment sooner with your veterinarian.
Anything else I can answer?