Probably a daft question, but we've had Covid in the house a few times with different people getting sick each time. Each time, others in the house have not gone on to develop it but have felt quite "off" or rundown.
Examples are being so tired we've fallen asleep in the day, or having issues with lymph glands or having chest pain flare up again that only occurred with Covid. All these happened when we had Covid in the house, but with the non-Covid household members testing consistently negative and not going on to develop proper Covid symptoms (so I don't think its a case of false negatives).
I'm guessing perhaps that we have all been re-exposed to Covid each time someone has it, but the non-positive people are fighting it off, which has caused these issues. I'm not explaining very well, but does that makes any sense?