Implantation bleeding

This was the month and cycle I conceived. Since I found out (I'm almost 35 wks now) I've been trying to decide if the spotting from January 23-25 was implantation bleeding. I got a positive opk on January 15 after about 9 days of high. My ultrasound said around the 17th was conception day so it was super close to what I thought! The spotting was super dark brown, it was on and off do you think that was implantation bleeding? This is my first baby so I'm just trying to be more educated for the second one if it happens again.