I Am On Pantoprazole Now For Over A Month, And

I am on pantoprazole now for over a month, and recently I have had lots of burping after any meal, and my sternum area feels very tight and tender often, as well as a light acidic taste in my mouth generally by early evening. What else can I do? I have already eliminated fatty and acidic foods and have dropped nearly 20 pounds over 3 months, and I am not an overweight person to start with. I tested negative for H Pylori and Barium test showed no sign of stomach or esophagus blockage etc.. What else could be happening?