Covid positive after recovery.

Sir please advice. I had fever on april 20 to 22 which had decreased with dolo. I took RTPCR on 20 april which came negative. After that I have done HRCT which showed CORADS 5 and CTSS 6/25. I took doxy and pulmo clear along with vitamin and limcee. I took another RTPCR as as doctor advised me on 27 which again came negative. I took HRCT on 6 th may which showed decrease in infection with CTSS 3/25. I only had mild cough throughout. For joining back to office I took another RTPCR on 9 th May but recieved positive with CT vlaue 29. I am very much confused. Presently I am having post nasal drip and very mild cough. Feeling discomfort due to lingering feeling in the throat. What should I do now. Doctor told me that RTPCR may be positive with dead virus also. Why I am not tested positive earlier and why I am testing positive now. Please clarify me. I am getting very tensed and anxious by thinking whether it is a new infection ? My temperature is staying around 98.2 to 98.7.