Plan B symptoms or Pregnant

So i had my last period around 1/24- 1/25 ending on 1/29. I had drunken sex on 1/30 so i couldnt really remember what happened. So that afternoon i had went to buy and use a plan B onestep jus to be on the safe side. About 5 days later i notice i was bleeding it was a redish brownish blood for about a day and a half around 2/4. I have been having breast tenderness and im nervous.