I am having upper abdominal pain. Cause? Can u explain.?

Many things. Your description is insufficient to make a diagnostic decision, but includes acid reflux, esophageal spasm, gastritis, gastric or peptic ulcer, pancreatic disease, biliary tract disease, colitis or colon tumor. More details and diagnostic tests are necessary to give you a more detailed answer. All of these possibilities should be ruled out by your physician as soon as possible. Don't delay.