Pain in my upper abdomen when drinking cold beers. Why?

A warning sign. Pain is your body's way of saying stop! Of course, not all pain signals something bad, nor are all therapeutic procedures painless. However, there is nothing therapeutic about downing a lot of beer into a stomach that hurts. A reasonable assumption is that your stomach is already inflammed, so beer just irritates further an already irritated stomach lining. Stop drinking, & please get evaluated.