5 days late, stress or pregnant or something else?

I'm currently 5 days late, is there a chance I could be pregnant or is it due to stress? I really don't think I've been stressed lately, I am not one to stress. I took a test on my 2nd missed day which came back negative, but I heard you can get a false negative during the week you're due?
I don't feel bloated? I know if I was due I would feel extremely bloated, but does one feel bloated when pregnant? I've felt nauseas 3 or 4 times this week, but I put that down to early mornings and lack of sleep (I get like this when I don't sleep well) Sorry for the many questions, I'm 21 and just worrying about it quite a bit. 
I've never been this late before, I'm typically quite regular!