Increased cough on 7th day of covid.

Hi, This is the query for my father, aged 66 years. He is bp and ckd patient. The ct scan showed 20 percent mild covid case. Till day 5 all the symptoms were almost reduced to nil, except weakness. On day 6 while he was on glucose syringe, his entire body started shivering and spo2 went down to 85 within 10 minutes. Then the doctor gave dexa and he became stable. After this incidenc his cough is quite increased, though his spo2 level is normal i.e. 96 without external oxygen support. He is taking vit. C, zinc, multi vitamin and fabiflu(favipiravir). From yesterday he is also taking dexamethasone injections twic a day. My query is, the increase in cough on 7th day could be a serious issue or its normal. Please prescibe some medicines/ rem dies for this. Thanks