What Causes A Delayed Period After Quitting Birth Control Pills?

I started birth control May 13th, the day I started my period. Quit taking it with the first 2 weeks because I could not regularly remember to take it. I am now waiting for my period to start. Im over a week late based on last months date. is that normal? I've taken a couple preg tests and they are neg but I have been feeling different lately. Nausia and headaches