I have low grade fever, that persists for 3 to even 6 months I cannot lead a normal life?

Hi, my name is (…). I’m 30 years old. Last 3 winters I have low grade fever, that persists for 3 to even 6 months. I have diagnosed Hashimoto’s and on eutirox medicine, with ups and downs of hormones. I’m told that fever can’t be from Hashimoto’s, but blood test didn’t show anything. I don’t know what to do. I’m feeling tired, sleepy… I cannot lead normal life.
Thank You very much!