My 4 Year Old Granddaughter Has Been Running A Low

My 4 year old granddaughter has been running a low grade and sometimes higher fever for the past 2 months...that we are actually aware of. During that time, she also did have a cold virus or 2. She is not quite as energetic as previously; but during the one virus she had, she was pretty sick and also complained of her legs being very tired. Normal blood work appears ok, but close to anemic. She has always sweated profusely while napping. I'm just getting concerned about a fever lasting this long...even though most of it has been low grade.