Implantation bleeding

Wondered if anyone can help. I've had mid cycle bleeding since feb (when I was still on the pill). Came off pill end of April and it's still happening CD20 every time for about 3days spotting/ very light bleeding. This time it was 3days after positive opk so can't be ovulation bleeding. Anyone still under investigation as had ultrasound which was normal. Anyone point is yesterday I had a tiny bit of red blood/discharge at 8DPO. Wondering could it be implantation bleeding. Never had bleeding at this point in month but my mid cycle bleeding only ended sat morning so worried it's just left over from then. Any thoughts/advice. 5days till period so too early to test!!