Why do I get diharrea after drinking alcohol?

Irritable bowel ?? Alcohol can stimulate irritable bowel symptoms of diarrhea. This could also be due to an allergic reaction. Best to see your doctor to confirm the diagnosis.
Gut inflammation. Alcohol has the ability to inflame mucosal membrane surfaces, such as the esophagus (gullet), stomach and the first part of the small intestine, and can also, with longstanding heavy drinking damage the nerves that regulate the GI tract. Both of these can cause diarrhea. In addition, heavy and regular use of diarrhea can lead to vitamin deficiencies (niacin etc.) which also can cause diarrhea.