Confused asf

Ja

So my period is 3 days late and yesterday I decided to take a pregnancy test and it was positive faint line but positive and I took 2 both a faint line. I got to the doctor and they test me and it’s negative . I go to the store and buy a clear blue test and it says negative . But how could yesterday’s test be positive and today be negative and I still no not have a period . Has anyone ever experienced this ?