are you having any bowel movements?? while your fasting..you should be having bowel movements EVERYDAY...if you are not ..you need to break the fast...or find a way to have one...you are autointoxicating with toxins and can die without this one very important RULE to fasting.... also ACV will fix your heartburn problem...your stomach is not clean ..thats why its burning ... the more alkaline your stomach becomes the less burning you will get....are you an experienced faster?? water fasting is only for the most experienced and healthiest of bodies.