Irregular spotting for nearly a week? What does it mean?

Deleted. • This app is absolute garbage and so are the people on it.
I've been spotting light brown with dark brown clots since Monday the 5th and I'm supposed to get my period in 4 days. I have my regular symptoms, heavier breasts, irritability, and light cramping. 
The first thing that popped into my head was of course implantation bleeding. How long does that usually last? 
It should be noted that I'm not on BC and we are not TTC. 
I simply don't see how this could be implantation bleeding. Before the other day, the last time my BF and I had sex on the last day of my fertile window (Oct. 2nd, unprotected until about halfway), but the last time we had sex before that was September 7th and my period came on September 15th.
I just think that's too early for implantation bleeding. I have been very stressed lately, so that could be a factor. I need to relax so if it's nothing, my period will come on time. I've stressed myself into being 6 days late before. I also smoke cigarettes. I'm worrying myself silly because this has never happened to me before.  Any insight is appreciated.