Pregnant but bfn?

[Chicken123]

I’ve read that women have been pregnant but tests haven’t picked it up until later on in their first trimester going into their second?

Has anyone experienced that?

It’s been 21 days now, potentially more, that I’ve been experiencing many symptoms and just overall feeling ‘different’ and just not right x

It's incredibly incredibly rare and more than likely because their hcg levels have got so high it throws the test off