When a dog stinks, there three main culprits. They are the teeth, ears and skin.
Teeth - Even if your dog is young, he can have serious dental disease or a foreign object stuck in his teeth. Even puppies should be taught about good dental hygeine. You can use a soft bristled tooth brush and brush his teeth. If you start it now, he'll tolerate it better when he's older. All dogs over one year of age should be taken in for regular dental cleanings to promote good health.
Ears - don't be afraid to look inside. If you see black stuff, it's probably not dirt. It's probably an infection.
Skin - there are tons of skin infections, fungal infections and other problems that can happen with the skin. You should see your vet for a skin scraping and checkup to rule out skin disorders.
And don't forget the anal glands. If the anal glands are full, swollen, leaking, it can cause a bad smell. Get your vet to show you how to care for the anal glands. They can be expressed at home after someone shows you how.
If your shampoos are not working, you should see the vet for a diagnosis and proper medications.
Let me know if you have more questions.