CD 9?

I'm on CD 9 and yesterday when I woke up I have brown blood, I know old blood. I was thinking it was because DH and I kind of got rough but now I'm thinking it's because I ovulated. yesterday morning with fmu I took the clear blue digital opk and it was at low this morning I woke up and took the opk and I am at peak. is that possible to already be at peak when yesterday it was low?