When should I be able to take a test?

I had unprotected sex last Friday the 13th. I missed a few birthcontrol pills the week before and started having a light flow for 4 days and stopped the day before having unprotected sex. I'm super worried about pregnancy as a possibility but since my birth control is a 3 month supply, I won't be due for my placebo pills for another month. When can I take a pregnancy test?