I think it could just have been a second round of side effects. But you should have reported it to someone, because you'd be a carrier for I don't know how long if it really was COVID.
I had something similar. The day after my second Pfizer dose I felt like crap..low grade fever etc. resolved within 24 hours....and then 3 weeks later I started feeling bad one night...had a VERY fitful sleep, waking every 45 min or so...not like anything I had felt before. Got tested that morning and came back negative....was fine by noon.
I wonder if there is some additional immune reaction a few weeks out when the vaccine has essentially “taken”?