In my experience when I got a positive, I had the faintest lines on pregnancy tests and then a "pregnant, 1-2" on clearblue digital. I've always believed that clearblue digital is one of the most sensitive tests.
It depends on lots of things, like how many day before your period you are (The tests are most accurate after you've missed a period and, if it's before your missed period, you could get a negative even if you are pregnant).
It also depends with the normal pregnancy tests how long you left it before you read the answer. Some tests after 10 minutes have an evaporation line so can tell you you're pregnant even if your not.
Another possibility is that you are pregnant, but the amount of pregnancy hormone is still too low to detect on some tests.
In my experience, even though I was pregnant, my lines never got darker and I had an early miscarriage 4 days after my period was due.
Only the doctors can give you a real answer, and I hope it's the answer that you're hoping for x