I think the general recommendation is to take another rapid test 24 hours later if the first one was negative and you feel ill. Theres a decent chance of a false negative, but two in a row is significantly more likely to truly be negative.

You need to be noticably sick for 2 to 3 days before you can test positive on rapid tests.

Rapid Antigen Tests have around a 15-20% false negative rate.

There’s a significant chance you have Covid.

you’re basically supposed to test a few times with like 12 hours between. it sucks because they are expensive and the govt only gave us a few freebies. seems like the kind of thing everyone should get in the mail once a week but we are in a hellstate. there are constant false negatives depending on many factors but the positives are almost 100% accurate. so sensitive you will often still test positive way after you are no longer contagious.

I thought I had Covid recently but it turned out to be the flu. It might really be something else.