TMI!!!!!! Help please

I had my baby November 4th 2017 and on December 5th I had to have a D&C; cause there was still placenta inside my uterus after a month not knowing and on December 6th I got one depo shot in my arm but the nurse didn’t do it right and didn’t get all of it in my arm so now today at 8am this morning I had cramping pain on my left side of my pelvis and then about 3 hours ago I had brown discharge out of nowhere when I wiped and after that had nothing else and I never had brown discharge on depo shot and I’m wondering if it could of been implantation bleeding cause me and my husband have been very sexually active I’ve been having lots of symptoms