They could have been false negatives, of course, but I suspect I just hadn't been training my immune system for many months and it wasn't prepared to handle the normal cold or flu viruses I would normally be able to handle otherwise. Since that period of time, I haven't come down sick since.
Not saying that covid is nothing to worry about, but it's something you might want to consider down the road. I don't know your situation or what health concerns you might have, but being too protective can have it's downsides as well.