vaginapagina | possible missed/delayed period?

Ok i'm a little concerned and have a few questions.

background: had sex on June 16th and the condom broke. I took plan B about an hour later, and followed up with the 2nd pill right on time.

This month i have also started to work out more regularly (5 to 6 days a week, mid to high intensity) and have hired a personal trainer. (don't know if this would be a factor. And also a lot of tension going on at home with the husband :o(

well normally i start my period on the 21st-22nd of each month. Last month i started the 24th, and this month now its the 26th, and nothing. I took a pregnancy test today and it came back negative. It might be too early but i took it anyways. I have another to take, if you ladies should suggest so.

So my q's are, why could my period be delayed? And also, i went last month for my annual and got BCPs, (he gave me Loestrin) i was waiting until i started my period to start taking them, but if it doesn't come and i'm NOT pg, should i start taking them? This wont be the first time taking BCPs for me. I took them on and off since 17.

Thanks so much for any help you can offer!