Period 3 weeks late but 3 negative pregnancy tests. tested one week after expected period too. what's the problem?

Missed Period: Pregnancy tests are usually accurate a week after missing a period. Most likely you are not pregnant but missed your period for some other reason. There are many reasons this can happen such as stress, dieting, exercise, thyroid problems, etc. Rarely a home pregnancy test can miss a problem pregnancy such as an ectopic. If you miss frequently, you should see an Ob/Gyn and find out why.