Hi Michelle,
I'm a coffee connoisseur, too!
The answer to your burning tummy may be caffeine after all! Coffee has way more caffeine than the other beverages you enjoy. Drip coffee per 8 oz.(light roasts have more caffeine than dark roasts) has 115-175 mg caffeine, Brewed has 80-135, Hot or cold tea has only 40-80, and Coke Zero has 34.5 per 12 oz.
Have you ever tried the low acid coffees that are now available?
If it really isn't the caffeine, though, it may be the acid. Coffee is highly acidic and if you are sensitive to acidic foods, this may be the culprit.
How are you with acidic fruits, like oranges, grapefruit and tomatoes?
Shay