Upper mid stomach "discomfort" (middle epigastric area) only when standing or walking, other symps: gas, gas stuck when trying to burp.?

Maybe GERD. This could be gastroesophageal reflux disease (gerd) which results from a loose lower esophageal sphincter and/or overproduction of acid. Also it could be the pancreas, peptic ulcer, gallstones, or hiatal hernia ( the top of the stomach protrudes into the esophagus). Your doctor will be able to to determine what the cause is. In the mean time you can try otc ant-acids to see if that relieves pain.