Is it because my fast is healing my gut and acid reflux?
Dr. Eric Berg would say that heart burn is causes by LOW stomach acid. I think I agree with him. If I drink too much water after a rich meal, I get some acid reflux (because the water dilutes the concentration of my stomach acid).
If you get it while fasting, there may be something in your diet that you can adjust.
In the meantime, try Gaviscon. It’s a tablet that creates a foam in your stomach, that should catch the acid before it ejects out the top of your stomach sphincter. You don’t need to drink water with it, so it shouldn’t interrupt your fast much.