Paranoid or Pregnant?

So I had sex on Halloween that resulted in me taking a Plan B. I was spotting from 11/8-11/11 and i had then started taking Birth Control on 11/11 too. My period was due on 11/21 and it still hasn’t come. I’m 13 days late and had sex on 12/3 and I’m getting nervous. I know Plan B can make you late and a combination with birth control can throw your body out of wack. I have taken 4 pregnancy tests (two were taken 7 days before my missed period and the other two were taken 11/25) and they all say negative. However, i have been having various symptoms such as Nausea, Backache, Dizziness, Migraines, etc. Should i go to the doctor? Take another test? Or should i just chill out and stop stressing?