still getting faint lines

Hey everyone, I got my first BFP on Wednesday 4 days before my missed AF today is my due date for my AF but so far nothing, however I've still been testing everyday and my lines on my tests don't seem to be getting my darker? Is that ok? I'm literally only 4 weeks today so is a faint line still relatively ok? Or should it be really dark by now? I've done 2 CB digi's both say pregnant 1-2 x