My dermatologist assured me that doxycycline does not effect birth control. anybody elses dr tell them this?

Your dermatologist is a liar. If you are on a hormonal type of birth control (i.e. pill, ring, patch, shot) you need to be using a back up method, like a condom. Tetracyclines (that's the medication class that doxycycline is in) interfere with hormonal birth control, rendering it ineffective. Go to rxlist.com or consult any drug book and it will tell you to use an alternate form of birth control. And I might suggest finding a different dermatologist... one who knows what drugs interfere with each other.