Do you think your first test was a false negative? it's supposed to be 15% false negative. Or your good antibodies kicked in fast enough to keep the load in your nose lower.
I keep a few of the more expensive tests that are amplified PCR, but for the home. Cue and Detect. They are supposed to be better at picking up early cases and smaller viral loads. but may cause false positives at the end... ie you still have remnants of virus, but they are not infectious.