What Causes Spotting And Lymph Node In Groin While On Mirena?

Hello- I have a lump in my groin (37yr old female) I went to my obgyn as I was concerned it was my mirena iud.. The did an ultrasound and showed it was in place. I have had the mirena for 1 yr with no issues but recently have had spotting. At time of spotting the lymph node gets larger. He put me on antibiotics and antianflam med. It seems it gets smaller and larger.. Do u know what it could be.i have had it for 5 weeks