Confused spotting or light Af???

Megan
I had a +opk on the 12/9 so ov'd between 12-36 hours after that. Af then should be due around now to the 27th
​Since the 21st I've been spotting. First day pink, then red on the 22nd and yesterday and today brown. Every time just in the morning only when I wipe never anything on my underwear. I usually do spot but usually just the day before Af not four day in a row.
​So has this been a very light Af or am I still wait for her to arrive. I have done some test but got bfn so now I'm 90% sure I'm not pregnant just wondering what happening this cycle. 
Anyone got any idea what my body is doing?