Late Ovulation - Implantation bleeding or not?

[JillyWillyPops]

I started using OPK's last month after ttc since dec. Turns out I ovulated late on CD20. AF was due on 3rd March but came 3 days late on 6th March. This has not been like my usual AF though. I normally have really bad cramps and headaches before AF arrives but this time I have only have light bleeding and hard to explain but like pulling sensations and light shooting pains. Could it be possible that this is implantation bleeding or should I just rule it out as a normal but pain free AF.

Thanks