I’m sure I’ve had COVID-19, why is the test showing I’m negative?

Rapid finger prick tests are accurate to around 90-95% so if the result is not what you expect you may want to take a follow up lab test that has an accuracy of over 99%. It could be that the illness you had was not actually COVID-19, but had similar symptoms. It could also be that any antibodies you may have had have worn off – this varies between individuals are we don’t currently know exactly how long they last.