28 days late

I'm 28 days late.. I've taken 4 pregnancy test and they were all negative. I've had period symptoms the whole time though. I did stop my birth control and decided to take it after my period to start over, because I kept missing my pill. But my period never came ! And the last period I had was very light, and only filled a tampon once. I'm not super stressed either. Maybe just stressed about not knowing what's going on but that's all. Help anyone ?