What Causes Pain In Right Side Underneath Ribs?

Hi I have been having pain on my right side right underneath my rib and it is an off and on pain. I went to the doctor and she thought i might have a gull stone so she sent me for an ultrasound but the ultra sound showed that there is nothing there. the doctor put me on a no fat diet and it is driving me insane and i want to be able to eat real food. i was just wondering if there is nothing wrong with mack toy gull bladder i was wondering if i can just go b my normal diet?