Reinfection of covid. With covid?

Hi, my father got his first dose of vaccine on 6th april, however he got high fever on 15th april..so we got him tested for covid and his result was positive, he had CT SCAN score of 8 which is moderate covid. He was on medications till 7th may. However his symtoms improved over the period of time, he didnt get any temperature for 6 days from 1st may till 6th may, his spo2 while he was covid positive was 92 but it ranges from 94-98 now, he doesnt have any loss of smell or loss of taste. He went out for 2 days after 7th in the evening for 1-2 hours for some work. From last 4 days,in the evening his temperature rises to 100.4 which goes down wothout taking pcm, the outside temoerature of the body is not hot but thermometer reading shows these values. We live in dehradun, it is still cold here. It has been 1 month since his first symtom showed, his spo2 is normal and cough has been improved too. the only concern is temperature in the evening. Is it possible to get reinfected with covid?