I feel tired and nauseous after eating is there a reason for this?

Check gall bladder: Post-prandial (after a meal) nausea can be a gall bladder problem. If it is nothing serious, it will likely resolve within two weeks. If it is associated with vomiting, fever, abdominal pain, then have it checked urgently. Try to avoid heavy meals, such as burger and fries, or any fried foods. Drink a lot of water. A high calorie meal will cause Insulin to rise higher and lowered blood sugar.