Most of the symptoms you described might be due to splenomegaly and hypersplenism caused by the mononucleosis. The pain caused by the spleen is located in the upper left quadrant, and can spread to the left arm. In hypersplenism the red blood cells are destroyed more often, thus causing anemia. Fatigue is one of the signs of anemia. The lack of fever indicates that the monoucleosis is not in the most acute stage. The hemoglobin in mononucleosis should be lower than normal, but if the laboratory tests were made in the beginning of the mononucleosis, then the hemoglobin is already out of the destroyed red blood cells, but not enough time has passed for the hemoglobin to be eliminated out of the body.