What Does Right Sided Pain In The Upper Abdomen After A Heavy Meal Indicate?

I have pain in the upper right part of my stomach 5 to 8 hours after consuming greasy and sweet or rich foods. For days, all I have had is an omelet before 2 PM and a tomato. I put 2 eggs, chees, pepper and onion. I have discovered over the last 2 weeks that if I eat before 2PM, the pain will be overwith before bedtime. The omelet doesn't bother me but I still have a lot of gas in my stomach (under my chestbone). If I eat any meals close together, the pain will come. It feels as if the food is getting backed up. If I eat a large portion or something greasy with additives at 7PM, for instance, the pain will wake me up at 1AM. It is excruciating,under my right breast. I have to lie on my right side and be very still.