Phlegm for past 1 month. Guide/ help.

I got this problem after Covishield 1st dose, & I was fully fit before that. After 2 days of vaccine fever and some medicines I was fine for around 10 days, but then phlegm started month back and I immediately consulted doctor after feeling suffocation one day (month back), who prescribed Prednisolone 10mg BD, Montair LC, Pantop DSR (blood reports had 1.45 D dimer earlier, which is < 0.27 now. Also Bilirubin total was1.9. My RT PCR came negative, but I did not get CT scan). Got relief for a week after medicines, but phlegm is back again now with constant urge to spit. No other symptoms apart from phlegm, tiredness & sometimes a little suffocation. Have tried all home remedies like turmeric hot water, mulethi, ginger & honey, gargles, Ayurvedic medicines, prescribed medicines etc but I am not getting permanent relief. One odd day I feel better and the other day it's again back. Worst thing is I don't even know what the issue is and why it all happened after vaccine. Please guide/ help.