Cramping af was late by 3 days

I'm 18 will be 19 in October and iv never had cramps before ... I had nexplanon implant for two years and had it removed in August I started my period right away once it was removed but I have had it out for almost a year now and I noticed my cycles are changing and I'm having bad cramps and lower back pain and iv never had cramps or any pain before!! And last cycle I had my period for 6days and its normally 4ish 5 and I'm on my period right now and these cramps are so damn bad :(