Help Please

I had sex with my boyfriend a little over a month ago. He put on a condom & im on birth control. I got my period on christmas eve and it ended the day after christmas. I thought i was fine until i seen that one of the pills im taking can interfer with my birth control. And im currently having constipation, headaches everyday, decreased appetite, and cramps. Im not in a place to have a child, and Im not sure if i should be scared, but i cant get a test until the 4th. Any help? Thanks!