I have badbreath for 3 yrs. Checked with dentist but no problem in my mouth. But my gums and tongue is dry.?

Pancreas. Pancreatic issues can cause bad breath. Check your c-peptide levels. Improve your digestion - take digestive enzymes before meals i like serropeptidase and betaine hcl after meals if you are <150pounds you need 1000mg >150pounds need 2000mg or more you can test see what feels better. If you cannot tolerate hcl add bromelain the bad breath should disappear in 72 hours if no improvement see ur doc.
Could be tonsils. Tonsil tissue lives on the side of your throat an behind your tongue. Sometimes debris and bacteria gets caught here and can really smell. An ENT doctor should be able to look and see if there is chronic debris. I have taken patients with really bad breath to the or and scrubbed their lingual tonsils free of this debris curing their bad breath sometimes permanently.
You're right. It could be that you're not producing enough saliva to clease your mouth out of smell inducing bacteria. Some medical diseases can cause this. Also antihistamines like allergy or sleep medication is a common cause. Try drinking more fluids, sucking on tart things like lemon drops and chewing gum.