If the pain subsides after taking anti-acids then it is unlikely to be the gallbladder. The usual course of action is to assume the digestion system because these days IBS is all to common. However, there are other condition to keep in mind such as Hiatal Hernia, which can mimic many condition.
There is a family of conditions: that of Dysautonomia. The best way to start reading about it is on Wikipedia
There is obviously many more things to read about but this is my two pennies worth. Even though all the blood test were in the so-called 'normal' range they should be a mixture of highs and lows. If they are all low then this may indicate a problem of mal-absorption.
I had a similar array of signs but all my GP could come up with was Chronic Fatigue Symptom. Living healthier and cleansing my system help reduce many of the symptoms and eradicate some altogether. However, some have stayed even though they wax and wane.