brown spotting HELP!!!

I am 6 days late for my period which isn't normal for me I am very regular. I haven't been stressing any more than normal I did get a cold which usually doesn't change anything in cycle.. according to LMP I'm 4 weeks 6 days pregnant.. although I'm a bit skeptical because I have taken 3 first response tests and they are negative.. well today when going to the bathroom I noticed brown discharge/spotting. Only when I wipe does it show and it only happened twice today.. any clue what this is? I'm waiting till Saturday to see if I start my period if not I'll make an appointment to see what's going on. This is so not like my body to do this.