Meant to get my period a week and a half ago but I didn’t, I had cramps but no period.

Today I got a dark brown blood come through with a little bit of red? Is this a late period or implantation? I had sore breasts 2 days before I got this dark blood come through? (My period is not usually late)

I had sex during my ovulation (not thinking) so I’m worried i could be pregnant.

I need some advice.