Any advice?

Hi ladies, 
I think I should have started my period today. I woke up feeling a bit queasy (I sometimes do) and thought I should take a test (clear blue digital) I wish I had not as it said 'not pregnant' :-( 
I have had REALLY tender breasts, a few chest flutters, tickley cough at night and thought it may be a possibility from things I have read.
Would I have tested too early or would it simply be that I am not pregnant?
Please be honest, thank you x