What Causes Brown Spotting With No Regular Menstrual Period?

I'm a 29 year old 5'4 that weights 195 women I had my period on the April 8 on April 21 I begin cramping so bad that I felt it in my butt with the cramping I started spotting I put on tampon and kept it on but nothing was on the tampon I spotted for that day and then brown spotting occured the next day and I only cramped half of the day on the 22nd I'm trying to see was that implanatation because the last time this happen I was pregnant with my 3 year old