Can Missing A Pill Lead To Pregnancy?

Hello,

I recently moved to Germany and encountered some problems getting my birth control prescription refilled, and therefore missed a pill. In the mean time, I had unprotected sex with my boyfriend, and now we're worried that I could become pregnant. The situation is a little complicated, but I will try to explain it as clearly as I can.

I forgot to take the last active pill of my previous pack before my period started. I didn't think it would be a problem because I assumed I would just start my period a day early, which I did. On Sunday, when I normally start my new packs, I took the missed pill and went to the pharmacy with my American prescription to get it refilled. However, they wouldn't accept an American prescription, nor do they have an equivalent with the same hormone dosage available in Germany. I had to go to the doctor to get a new prescription, but it took an extra day and I ended up missing another pill on Monday. I finally got an EU prescription, but it's for a brand with a slightly lower dosage (1 mg Norethisteron/0.02 mg Ethinylestradiol vs 0.5mg/0.02 mg). I took Monday and Tuesday's pill as soon as I got the new pack, and because my boyfriend and I are worried that I could get pregnant, I also took Sunday's pill of the new pack. Is there still the chance to get pregnant?