8 days late negative tests

You didn’t ovulate when you thought you did/when the app predicted. When and if we ovulate ultimately determines when and if we’ll get our periods. If you ovulated later than expected, this will cause your period to show up later than expected. Same goes for a BFP. Most doctors won’t perform a blood test as a way to confirm a pregnancy because it’s not necessary in the vast majority of cases, especially since HPT’s are very accurate, less expensive and less invasive!