What causes liver pain after overeating?

Sure it's the liver? Pain in the liver area after eating could actually be from the gallbladder. Stones in the gallbladder can cause pain after eating, usually about two hours later, and particularly after a more fatty meals. You may need some blood testing and an abdominal ultrasound to assess this.
Bloating or stones. Im not sure how you are defining "liver pain", but abdominal distention and bloating can occur after overeating, and visceral distention definitely causes pain. If it's RUQ pain after you overeat, you may just be having biliary colic. So, i suggest you avoid big meals, and keep a food diary of this pain as it relates to meals and types of foods. Discuss with your doctor. Good luck.