I have a very fast metabolism and I feel very weak after 2-3 hours of every meal?

I have a balanced diet, my problem is that I feel very weak usually after 2-3 hours of every meal, I have also measured my BP on a few instances, and it measured - SYS - 100 to 110 and DIA - 55 to 67. I have consulted a few GP's here in my city, but no one is able to give a proper solution to the problem. Can any one help me out