can someone please help answer my question!!

I switched birth control brands and this new pack has a full week of sugar pills where my last pack only had four. I just recently finished my first pack and never got my period, I am not finishing my fourth day of the new pack and have a thick white discharge (something I typically get a few days before my period). Should I be concerned of pregnancy or is it just my body getting used to the change in hormones due to the change in birth control? I know that is most likely he cause but I'm still alittle nervous. (I use birth control along with pull out)