Since December... Negative test still 😳😳😳😳

I haven't got an period since December. I've taking test after test from first response to digital and nothing not even a faint line i go to the doctor on the 25 of this month to see what's going on but I'm thinking the worst... Bc if I'm not pregnant why hasn't af came! This didn't happen with my daughter... I'm freaking out! How about y'all did any of y'all have negative pregnancy test but still was pregnant