As some of you my/may not know I got my BFP on wednesday afternoon. Althought very faint they were there!

Yesterday morning I did a CB Digi and this came back 'not pregnant'
Anyways, I did a First response ultra early (can test 6 days b4 AF DUE) yesterday afternoon and got another very faint line within 3 mins and got up this morning and did another FR with FMU, anotherfaint line but a little stronger than yesterdays.
I should be getting a stronger line by now shouldn't i? Shouldn't my HCG levels be getting stronger by now?
And why didnt the Digi Pick it up?
Im phoning the docs at nine to book in but I'm wondering if anyone else has had this problem?

to all.