Pregnant for a Minute ?!

AF was 3 days late, so i took pregnancy tests and they were all positive.  To add, i took a blood test and my HCG was 24 and it didnt double the next day and bam AF arrives. It was a Chemical Pregnancy.
Has anyone had Chemical Pregnancies due to Glow asking to take a pregnancy test 3 days early than AF due date?
I still do not understand why Chemical pregnancies happen? The doctor embarassed me, she said its "fake" and that i rushed it.
Horrible choice of words...