What Causes Pain And Discomfort In Upper Abdomen?

I have had upper abdominal pain/discomfort for a few months now. My mother had stomach cancer and colon cancer. I ve done a Ultrasound - Abdomen and CT Abdomen and Pelvis. They found a solid lesion of the liver which measures 2.0x1.9x1.6cm. I ve seen the Doctor and he told me that the Liver will not cause the discomfort/pain I am experiencing and he can t think of anything else that could be the problem, I should just go on and don t worry about it. I am worried about it and am thinking off getting a second opinion. Any advise would be appreciated. I am not a drinker and do not smoke.