Implantation bleeding question

Anyone on here experience implantation bleeding that can tell me what it was like and how long it lasted? Yesterday I started spotting and today I am still just spotting, it is a little darker today but more like what I see at the end of my period in terms of coloring. I only see it when I wipe, and nothing on my panty liner. AF was actually due to start tomorrow so I'm not quite sure what is going on, I just know it's not normal for me to spot like this... any help would be appreciated!!!