Chronic bad breath. dentist says my mouth is healthy. i drink enough h2o and have healthy diet etc. what should i have dr check - sinus, stomach etc?

Breath: Assuming no gum disease (2nd opinion?) it may come from the stomach. First i would try probiotics like yogurt for 2 weeks and see if that solves the problem if not then see a GI specialist or a dentist that specializes in bad breath/halitosis at a local dental school perhaps or call the local dental society for a referral.

Chronic bad breath: Poor oral hygiene, gum disease, sinus infection, acid reflux, smoking and diet are the major causes of chronic bad breath. Also systemic or bowel diseases. If your dentist has ruled out dental problems, you should see your physician or an ENT specialist for an evaluation.