Sometimes it's the additives in food and drink that can cause heartburn. Like citric acid, for example. Some carbonated beverages cause it for me, too. Too much dairy can trigger it as well. I agree, cutting one possible culprit out at a time and seeing if it makes a difference is the best way to go.

In the meantime, I've found that a teaspoon or two of apple cider vinegar helps calm my heartburn almost instantaneously.