What Causes Vomitting After Food Consumption In Kids?

Hi...I have a 7 year old son, who over the last two weeks, will sometimes vomit after dinner. He will complain that his tummy is full and it looks to be very bloated and hard. He is completely fine during the day as far as his eating and being able to keep the food down, it is only after dinner. Sometimes the vomiting will last for hours after the first episode. I am very worried that there could be something seriously wrong with him. Any feedback you could give me would be greatly appreciated! Also, plan on scheduling an appt. with his pediatrician today.