what's going on?

Okay so I'm not due til November 3rd and I had unprotected sex October 20 the day after ovulation supposedly and on 27th to 30th I've had red brown spotting but it would only be a little bit and then stop and also on and off cramping like I'm going to start haven't tested yet not sure what's going on I know when I start bleeding it's a lot on the first day so I'm wondering if It can be implantation or am I just crazy.