TTC...

Is it possible to not get pregnant even when you have sex during your fertile window? Me and my SO have been trying and we've had sex several times this past month and not just during my fertile window. I took a test a couple days ago and it said negative but I figured it was too soon even though it was a clear blue test that's supposed to be able to detect a pregnancy 5 days before a missed period. I figured I'd wait a few more days until after I actually missed my period because it seemed impossible to not be pregnant and I've been having pregnancy symptoms, I was pregnant once before so I know some of the signs and feelings. Well last night I went to use the bathroom because I was having a little cramping and there was blood in the toilet so now I'm thinking I'm either starting my period 3 days early or something is wrong.... My SO and I really want to have baby and my last pregnancy with an ex of mine wasn't planned so I just want my next one to go the way I want it to because it will be planned which means I'm going to be nervous about everything.....