Implantation Bleeding or something else?

Katy
So from all the research I have done implantation bleeding should be 6-12 days after conception, but at 4 dpo I had a brown discharge, some cramping, and a backache that has lasted 2 days now. I have no idea what is going on down there, I have had ovulation cramps before but not like this and not after... Has this happened to anyone else?