It is important to understand what is causing the low fever to not go away, many of them are caused by viruses. You can go to the hospital for a blood test to see if the white blood cells, granulocytes, neutrophils or lymphocytes are high or low. If the fever is found to be viral in origin, a fever of 4 days is also a normal condition, and you can take an antiviral oral solution or antiviral medication to relieve the symptoms. Because virus-induced low fever can recur, some last for about 1 week. At home, you can disinfect and ventilate with vinegar fumigation.