Reoccurring fever with fatigue. Come?

Hi Doctor, My father suffered high grade fever with cough and running nose on 2nd Sep. Next day after consulting a doctor he took Meftal for 3 days. Till 17th Sep he was having fatigue, cough, sometimes cold and also sometimes low grade fever (below 100°F). On 18th (after 17 days from first symptom) high fever again came which wasn't going down with paracetamol. All the test were done on 25th Sep (Malaria, Dengue, Typhoid, Chest Xray PA, Haemogram, Urine RM) and were normal expect Total Leukocyte Count which came 2400/cumm. ESR was 2. Again high fever came on 28th Sep (27 days from 1st Symptom). Spo2 level is around 95.What should we do is this a worrying situation? Today is 28th day from 1st symptom. If this is corona, how long it takes. Even after 28 days complications can come?