What Causes Abnormal Vaginal Bleeding After Taking Plan B?

me and my ex boyfriend had sex August 28th. that day we did it 3 times in one day. he came in me all 3 times. then on the 29th we had sex again, he also came in me that night. Then on August 30th,i went and got the Plan B pill.

Then yesturday night we had sex, again he came in me also. Now like about an hour ago (maybe) i started bleeding..idk if its my period. idk if its spotting, or idk if that means im pregnant..and its not heavy bleeding. it looks like what it would look like when i get my period