Very confused. . .

Went to the er today for some vaginal bleeding(baby seems to be okay. Supposed to be 9 weeks according to last af. Had ultrasound pelvic exam and vaginal ultrasound. They tell me I'm 4 weeks. The problem I'm having is... I took a clear blue weeks estimator on March 12th and it said 2-3 weeks. Meaning 4-5 weeks that would put me at a minimum of 6 weeks. And a maximum of 7 weeks. So according to the test and what the doctors are telling me I knew I was pregnant 2-3 weeks before I was actually pregnant. I'm so confused about this is unreal. Can anyone help me to understand