Low grade fever post covid. Treatement!

My father ,age 60 years was admitted on 17th april for saturation level dropping to 50 , he was treated for 60 days in ICU (had tracheostomy tube inserted and also spent around 40 days on ventilator support) he was discharged on 17th june , he was tested negative on 20th may, it has been over 3 months ,he tends to get low grade fever 99 to 99.8 in evening and settles on its own without giving any paracetamol, he is having severe weakness as he lost around 30 kgs in hospital Chest X-ray, ultrasound,urine routine,urine culture, blood fungal culture, blood culture,CBC all tests done And normal, haemoglobin level is 9.3 and tlc is elevated at 13200 . Spo2 level currently stands at 90-95 without using any supplemental oxygen.also he has sleep apnea problem from last 5 years for which he is using cpap at night.Please suggest if the fever is normal and if not how to proceed treatement