Could I Possibly Be Pregnant? I'm Supposed To Start My

Could I possibly be pregnant? I'm supposed to start my period Oct 1st. Saturday night I had bright light blood then yesterday it was like blood and discharge mixed together, but there was only a little bit on the wipe I had used. After that I have had no bleeding. Now I'm just having white/yellowish discharge. I have had menstrual like cramps, I feel pain on my left and right sides (they feel exactly the same way as if I was already on my period), and my breasts are tender, but they usually get that way before my period sometimes too. I also took Plan B about a week ago. Now I know some women bleed after taking Plan B in about a week and it can also mess with your cycle. I just need to know if maybe I'm just spotting because of my period, or because of the plan B or if this is like implantation bleeding?