I don’t understand…

I stopped my birth control in January, had my period 1-11 through 1-15 and then started TTC. Today according to my app I’m 3 days late.I tested the day I was late and got a very faint line. Bought a digital and it said pregnant. Well now it’s two days later and my lines are still like hardly there when I test with line test. Maybe I ovulated later? But still shouldn’t the lines have got darker since 2 days ago? My appointment is on the 15th with the OB