Feeling tired after a big meal is a normal part of being human. Your body wants to slow down to properly digest the meal....and that means sleep. Some foods have been known to induce sleep and are a better choice than pill types of sleep aids.
Warm milk has a sleep inducing effect. I have not personally tried it since I am allergic to milk. Other foods are peanuts, sunflower seeds and oatmeal cookies. So technically a warm glass of milk with some oatmeal and raisin cookies should put you right to sleep.