Implantation bleeding at 4DPO?

Emily • My cute hubby is 25 and I am 22. We made a cute person named Thor born on June 29th!
Hello ladies! 
I have a 45 day cycle and I am currently 4DPO. I know implantation bleeding usually happens 8-12 DPO, however I went to bathroom this morning and I had a very small amount of pink\light brown spotting. Is it possible for me to have implantation bleeding so early? I have also had very tender nipples, which is rare as I usually have tender breasts, not nipples. Has anyone else experienced this?