Which is best for Breathing difficulty.

I was affected from Covid 19, but I not faced any breathing difficulty and within 10 days I recovered from it. But after 15 days I started developing shortness of breath. Then I consulted a doctor who given me budate 200. After using it for one week I not found satisfactory results. Then another doctor recommended me deriphylline , again my condition not improved. Then I consulted pulmonologist who suggested me AB phylline for 15 days. After using AB phylline I got good results. Then again after 15 days when I stopped taking it after 4,5 days of stopping it again I am feeling same. Now it's been two months I recovered from Covid but still i am having some breathing difficulties 2,3 days in a week. I am confused which Medicine I continue for long for better results. Please guide what to do