How long does implantation bleeding last? Been spotting for 6 days now and I don't know why.

I've read that it typically doesn't last longer than 2 days, but it was the first thing that popped into my mind when it started and now I'm making myself nervous. 
Light brown discharge, usually creamy but also clear and stretchy with flecks of brown at times (think ovulation consistency). I've also had a few brown clots. Scant for the most part, sometimes makes it to my panties. Sorry if tmi. 
I feel like it's just old blood, but I'm due for my period in 5-6 days and I think it's a little late for that?
Not on BC and we are not TTC.
I simply don't see how this could be implantation bleeding, since 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 was September 7th. My period came on September 15 and then we didn't have sex again until October 2nd (simply due to life getting in the way). 
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. Any insight is appreciated.