4 days VERY light brown/reddish pink spotting

Very regular 28 day cycles and I'm on cycle day 41 now. I have on and off VERY light brown/reddish pink spotting for 4 days, I only notice it maybe 1 or 2 a day and only when I wipe, no need for panty liners or anything. The consistency changes from very mucosy to sticky. 
I tested today and got a BFN. No signs of AF. Could this be pregnancy and a false negative?