It'd be good to record when you feel this way in a diary for your next drs appt. There may be several reasons for the full feeling. Your doctor will help sort it out. I have strictures in my small intestine and get feeling full quickly if I've clogged myself up with too much fiber trying to get through there.
Eating less because you're feeling full may make you end up losing weight gradually, too.
Let us know what you find out. I'm sorry it feels like a punch in the gut. That's an apt description of how I've felt, too, many times. Good luck to you.