My little guy Ralphie had some really bad dandruff when I got him, I use Biogroom shampoo and conditioner and eventually got rid of it, but it took some time. Some baths were conditioner only. I think it's really important to rinse really well after you shampoo and always use a conditioner because it conditions the skin as well as the hair. Use shampoos especially made for dogs, but I've heard some say here, that you can use a human conditioner. I personally wouldn't shampoo more than once a week. What bothers me about your case is that you say there is an odor to it and this makes me think it could be a yeast infection or something serious, so many a vet visit would be in order.
Lately, I've been reading that oatmeal can be irritating to some dogs, so I don't think I would use it and don't use human baby shampoo, it's really strong because it's meant to fight cradle cap. Here's some good information on fish oils and dosage.
Fish Oil: The Dangers of Too Much | petMD