How many dpo are you now?
It's really tough to say in the early days and first couple of weeks, because so many factors can dictate how dark the line is. To be honest this is why I don't test once I've had two or three positives in the first couple of days, because it messes with your head so much! I completely understand why you are testing though. If at all possible I'd try to stop testing and think positive for now until you're given a reason to think otherwise
Oh and digitals are not very sensitive at all, so I have heard of many women getting positives on other tests and digitals taking longer to show 2-3 weeks or even be positive at all.