5 Answers

Are you eating foods with a lot of sugars in them? Cut the sugar. You may be eating too much. Try yogurt and a protein bar. 

All of the above and in my case...which could be yours...make sure you are not eating anything you are allergic to.

Eat a lighter meal.....

Everyone feels tired after eating. Eat breakfast like a Prince, lunch like a King and supper like a pauper. I say this as lots of business men go home eat an enormous meal and then go to bed - the food doesn't get metabolised properly and then the next morning get into their cars I've seen many of these men who are overweigh. Take more exercise perhaps. Take Vitamin C at breakfast time for energy also helps in the winter.

You could be a border line diabetic.  Carbohydrates cause a in balance in sugars and induce a need to sleep and fatigue after eating . If you are eating mid day try eating less carbs and eating something less complex for easier digestion