I Had Unprotected Sex Last Week Took A Plan B

I had unprotected sex last week took a plan b within 12 hours after, I was doing some research on the plan b, and it stated it's less affective if you are over 165lbs. At the time I was 180lbs. I saw some bleeding or spotting today. It went from light to heavy back to light. It's only noticeable when I wipe myself. My expected period is supposed to be August 5. Therefore if it is my period it's 13 days early. Is this considered my period despite the weight issue?? Was the plan b affective?? (B.T.W. my menstrual cycle is all out of wack the last period I had was may 21 till may 27)