My boy, Beethoven, is about 6 months old. I bathe him at least once a week, maximum every three days, but he always looks dirty. He has brown spots everywhere, and the fur between his eyes and above his nose is an icky brown/green colour. I use a Burts Bees shampoo for kittens and I put olive oil on him after a bath for his dry skin. Am I doing something wrong? Do I need to order a special shampoo for him?