What Causes Bleeding After Taking Flucloxacillin While On Mirena Coil?

Hi there, I have had a Mirena coil for nearly a year and a half and have had no bleeding up until now. It started last week when I was taking a course of flucloxacillin (2000mg per day) for 5 days. Are the two in any way related or was it just an unlucky coincidence? I'm also getting bad cramps. Thanks very much in advance for your help, Christina