Implantation or nah??

So my cycle is very irregular and I'm not that in tuned with my body, so I don't know how often I ovulate. But on Monday I started spotting brownish and really light pinkish. It looks like implantation bleeding, but it's Wednesday and it still looks like that. I'm having dull cramps and my lower back is hurting down to my thighs. How long does implantation bleeding suppose last?? Or is this just my cycle??