new discharge w/Mirena

Ev
so I got my Mirena placed last August and it's been really good too me, last time I had a period was in November and now out of no where on Friday I noticed some light brown discharge in my underwear and now it's Monday and its still around! 2 weeks ago I took a pregnancy test because I was having some extreme soreness in my nipples and that's not a period symptom for me but it came out negative... also on Saturday I had cramping but that was only one time, should I be concerned?