Why is my BFP so faint?

on the digital ones they show up pregnant...but why on the 1st response and clear blue they are so faint you can barely see them? i'm 2 days past when my AF was due...shouldn't they be a little more bold at this point? i know it depends on HCG levels, so it kinda makes me worry that something might be wrong... and YES i'm stressing. but my 1st pregnancy it should up very clear a week BEFORE my AF was due. now days after, its barely visible!