Could be gastritis - sounds just like what I've experienced. Gastritis doesn't have to be all that severe for it to cause all sorts of weird abdominal and chest discomfort - you can really get it anywhere in the chest and abdomen, along with heart burn, heart palpatations, bloating, naseau and vomitting in severe cases.
Accute pain on the left side of the abdomen is associated with pancreatitis, but it sounds like you've been checked for it. I also had this and it was part of my gastritis (diagnosed as very mild). Try cutting out caffinated beverages, alcohol, smoking, fatty foods and tough to digest foods, including bananas. Also, try not to focus on the discomfort; this is sometimes the best medicine. For my self, focusing on the problem only seems to magnify it.
You could also try flushing. I don't know if it will help with your specific symptoms, but it's certainly good for a lot of other things and is worth trying. It really opens the doorway for good general health.