Possible implantation

About 3 days before my period was due, I had some reddish/pinkish spotting. I just thought it was my period starting. Now I have a very light brown discharge. It's inly there when I wipe, not heavy enough even for a liner. My period is due today at the latest as it is cycle day 31. Do you think this is just a really light period or implantation? I've been having cramping intermittently only on the right side. My periods are usually very heavy from the start because I have PCOS. What do you think?