Implantation Bleeding?

Liz
I've had unprotected sex with my boyfriend, and the last time (he's out of town) was 2 weeks ago when I was "most fertile." My period wasn't supposed to start for another 7 days but then I get this.
Blood is a mix of dark brown and red, lots of mucus (mostly mucus!) and some clots... it's the consistency of a rubber band! Super light flow... only enough to fill half a tampon in 24 hours. On my second day of this.
Is this implantation bleeding? Or a weird period? Please help!
Thanks!