Bfn after 4 days of being lateeee!

I am 4 days late and I have a 28-29 day regular cycle so I'm on CD33! 
For the first time I've never been this late,
I have mild cramps here and there... No signs of a period, 
Can it be too soon for a positive ? 
Has anyone experienced this and got a positive on the pregnancy test after a few negatives ???