Getting worse again on 4th day of antibiotics?

I've had bronchitis for about a month and 4 days ago my doctor decided to put me on antibiotics. it helped a lot the first couple days and i felt almost completely better. I had been coughing up a lot of yellow mucus before I started the antibiotics and that had stopped. But today i woke up feeling slightly worse again. not too bad but it still worries me. I also coughed up a big wad of yellow mucus which i haven't done in the past 4 days. this this ok or are my antibiotics not working anymore? I also started my period today, could that lower my immune system or have anything to do with it?