Periods Not Due But Then Why Experiencing Cramps, Backache Along With Spotting?

Hello, i am not due on my period till around the 19th to 22nd of febuary and for the past two days i have had really bad cramping,backache,hedaches&dizzyness and very bad mood swings and today i went to toilet and noticed a brown/pink dot at the top of my pants, i was just woundering what this might be?? Plus i had the implant took out in november and on 19th/22nd it will be my 3rd period..