Why does my stomach hurt so bad after drinking diet pepsi?

Why drink it then?: I can think of lots of reasons why you may be experiencing an adverse reaction to a carbonated beverage that contains multiple chemicals (artificial flavors, coloring, and sweeteners). May I suggest you try drinking water, and assessing your response. My answer then becomes quite different if your stomach pain is limited to Diet Pepsi or is generalized to all liquids and ingestants.