Without being able to see your dog in person, it's pretty much impossible to tell you why he's smelling the ways he does or what could possibly be causing it. The list of things it 'could be' is nearly endless: allergies, infestation of parasitic mites (mange), thyroid problems (although he's awfully young for that!) or a bacterial or yeast infection just a few. From your description of the fact it never really goes away, and the smell, I suspect it's a yeast infection. Sadly, this is one type of infection that gets worse if the dog is thick coated and frequently wet...because yeast likes to grow in dark/wet places, so the bathing you've been having done, could actually be making it worse...My suggestion is to call your regular vet in the morning and schedule an appointment for them to see your pup and see what they can determine. They'll most likely do a skin scraping of the affected areas (where they use the edge of a scalpel blade to gently scrape off the top layer of skin, looking for any mites), and possibly run some blood work to see if there is a thyroid issue.