Answer

Hi
It sounds like you are having a very trying time. I feel for you.
The odour sounds like it is originating from either the skin or the anal glands (anal sacs). There may actually be a link. It is interesting that you felt things improved initially after the vet emptied his anal glands. We must consider this significant. Also the fact that he licks himself constantly is significant.
I think there are two strong pssibilities here. First is that the anal glands are the central problem. These sacs are basically scent glands and when they do not empty properly the dog will often lick at them to try to get relief. The smell from the glands is then transferred to the mouth and then to anything that he then licks...this can be you, items of furniture and of course his own coat. I see this regularly in dogs....bad breath and smelly coat with impacted anal glands.
The second possibility is that the sebaceous glands in his skin are overactive and there is excessive oil building up on his skin and coat. This binds down the dead skin layer and it is not shed correctly. This dead oily keratin layer is an excellent breeding ground for the bacteria and yeasts that normally inhabit the skin. As these organisms break down the oil it takes on a nasty smell. The condition is usually termed seborrhea oleosa. Sometimes the dog will get quite itchy with this condition too (seborrheic dermatitis). Now this condition often goes along with anal sac impaction problems. The condition is more common in dark skinned dogs...I see it a lot in Dachsunds. Dogs that have overactive sebacious glands often have overactive anal glands and vice versa....the two types of gland are related.
So what do I suggest you do? First you should consider having the anal glands removed. If they need expressing monthly it is probably a wise thing to do anywhay as they are prone to infection if they swell consistently. This is not a big operation. Vets do it regularly. It will totally remove the anal gland possibility as a cause. Well worthwhile!
Secondly, if you suspect the skin is the primary problem (seborrhea oleosa) then you need to use a special shampoo called Malaseb (http://www.malaseb.net/). It is available at your vet and also on the Internet. It will lift off the top dead layer of keratin, cleanse the pores and control the bacteria and yeasts.
Obviously the Malaseb option is much simpler to try first. But I am suspicious the anal gland removal is more likely to generate a response.
I hope I've been of help here. Please contact me back if you feel I can assist further.
Kindest regards, Peter