Brown old blood after sex. TMI picture

SO and I just had sex. He started in top and kept moving around like putting my legs up on his shoulders and what not then we ended in doggy style. I got up to go to the bathroom and noted quite a bit of brown blood. My period is suppose to start Saturday. Is this brown blood (I know it means old blood) just the start of my period and he just knocked some loose or whatever? He's a pretty decent size and my vagina is a little shallow. I've had some before after sex but that would be right after my period not before. Also been ttc for about a year and a half if that matters.