For last 6 years i have a tummy problem whenever i left something heavy, i get tired, lazy and sleepy.help?

After lifting something heavy like more then 3-4 kg I get ticklish feeling around the belly on, after one day or even same day, i get tired, sleepy, agitated and lack of concentration, i cannot even do simple addition... i went to my G.P for check up he sent me for Ultra sound scan and they could not find anything abnormal... can any body know what might be the cause or how to cure it????