How reliable are tests before period due?

Lexy
Hello, I'm just looking for opinions really, my af is due in 2 days and I had 'that feeling'  for a about 5 days now I tested yesterday it was a BFN and even though it's early to test I can't help but feel really disappointed.  Do you think there is still a change of a BFP? I'm so impatient and eager, been having cramping that I'm really hoping isn't af :) TIA x