HELP!

I got the Mirena IUD back in April of 2018. My periods have been regular, but fairly light (I really only need a panty liner or a light pad now), and they last almost two weeks. I get the regular symptoms of cramps, sore breasts, PMS, etc. Well i started my period on January 5, and it was doing what it normally does. After I had sex, my period stopped on day 6. I’ve very very light spotting since then and my boobs still hurt and i get cramping every now and again. Does anyone know what this could be? Is it just the IUD or should I break out the pregnancy test?