For people who've had gastric byp surgery,?

I had gastric byp surgery in march 2008,and am just starting to eat full meals,but after about ten minutes i start to feel very ill,tired with no energy and even nausea's feel like ping out(feel like im drunk),sometimes i actually do!! today after eating a burger i got so tired i fell asleep,this used to happen after eating ice cream,soda etc. and figured it was a Sugar crash but now it happens almost every time i eat,What could be happening?