Hunger soon after eating can quite often be either:
1. a result of high sugar levels -your body sending a signal of hunger because its cells can't get the sugar it needs from your blood
2. if you're on insulin, a result of low blood sugar levels
If it's high sugar levels, it's a bit of a pain and usually the best thing you can do is resist eating more and instead take a walk which will help your insulin to get the sugar from the blood into your cells.
Ed