You might ask your GI if he could order an Upper GI to determine what is causing your discomfort
I have several types of chest pain, and I also have a large Hiatal Hernia, resulting in GERD, which can cause me chest discomfort. Just a thought. I hope your Doctor can find something to take, you mentioned Zantac, I used to take that.
Good Luck with your Doctor.
Best to you