What Causes Sudden Periods?

Hello there. I have a question. For 5 days ago I started to take penicillin, for my infected toe… the problem is now I have started to get menstruation, I’m on p-pills and I should only have my menstruation in one week, I have never tried to have period before time, and one week before is quite early! Can this be because I’m on penicillin or should I go the my doctor to check it out?