What might cause me to run a fever of 100 to 101.8 only in the evening. I don t run one during the day. I do have fatigue, but otherwise feel ok. I just had abdominal surgery in July. I ve had my surgeon check me & now I m going to a hematologist as some of my blood tests are a little low...hemaglobin, red & white cells, iron and potassium. i had a UTI when this first started, but took a round of Cipro and the fever continues. The hematologist wants to do a bone marrow & I want to try to treat the problem first without it. thank You, Jackie