I know it's been some time since you've posted but I was just thinking about your surgery and the scar and it occured to me what might be happening. Your stomach shrank during the fast. Now that you're eating again (and have been for months), the stomach is exanding to accomidate the extra food. I bet it's the expanding which is causing the discomfort.
Hope you're better now! :)
PS I'm going to feel like a dork if someone already thought of this. lol :)