Hey J.,
I also had a HUGE surprise last year when I found out I was pregnant while on birth control. And when I found out I was already 17 and a half weeks I thought it wasn't possible I had not missed one pill and I didn't have any other sympthoms other than I started getting heartburn.
I had been sick so I had taken all kinds of cold medicines and I had hurt my back so I had taken some muscle relaxers. When I found out I was pregnant they told me to stop taking the birth control right away. I wrote a list of everything I had taken and they went through the list and didn't seems worried about them.
My daughter was born a few months later and she is perfectly healthy.
I wouldn't think the medication you are taking would be to harmful to your fetus since they allow you to take it while your breast feeding. But if your worried I would just stop taking it or call your pharmasist if you can't get into the doctor right away.
I have actually talk to a number of women who have gotten pregnant while taking birth control and have had normal pregnancies.
Good Luck.
D.