ok mom's I need some help. my lo is almost 6 wks old and me and my so had sex for the first time…

ok mom's I need some help. my lo is almost 6 wks old and me and my so had sex for the first time about 2wks ago. (did not use protection stupidly) I thought I was having my period this morning, looked normal, slight cramping, but this afternoon it's pretty much stopped except for some brown discharge. could this be implantation bleeding? or are the first period after having a baby weird?