little more than 3 weeks late on my period and I finally got it yesterday. i took a pregnancy test…

little more than 3 weeks late on my period and I finally got it yesterday. i took a pregnancy test three times, all came out negative but i know when you are breastfeeding it could result in a false negative. I have extremely heavy bleeding and aweful cramps. do you guys think i just got my period or a miscarriage?..