Just Started Birth Control Pills 2.5 Wks Ago, Now on Period

My boyfriend and I have been together for a couple of years now, and after our third broken condom -- followed by yet another round of Plan B -- I decided to go back on birth control pills (this is the fourth kind I have tried, hated the first three). My gynecologist prescribed Natazia, so I began taking that 16 days ago, two days after I took Plan B.

One would think that the Plan B combined with the birth control pills would throw my period seriously out of whack, but I got my period today ... which was the day I was scheduled to get my period before I started the pills (so I had a normal, non-birth control period 28 days ago today).

I was under the impression that we could begin having sex without condoms after this birth control pill pack is over, but now I am concerned that the hormones have not affected me and my cycle yet, thus leaving me susceptible to getting pregnant. What is going on here?