I'm 20 i had sex on 26th august and had unwanted 72 on 27th august. today is 6 september. i was having very less brown spotting from 2 days but today i bleed. i'm tensed why am i bleeding? am i pregnant or just hormonal changes?

Bacterial vaginitis : It is possible you might be pregnant, but too early to tell. It is most likely an infection. You need to see your gyn to evaluate what is actually happening.

About Unwanted 72...: Plan B, Unwanted 72, and other brands of emergency contraceptive pills are hormone pills and can alter the menstrual cycle bleeding for the cycle in which Plan B or Unwanted 72 was taken, and sometimes the next month's cycle too. One should be sure to check a home pregnancy test about 3 weeks after sex, because emergency contraceptive pills work most of the time, but not all the time.