Clear discharge with a stream of bright red blood.

Okay so I'm 17, I've had 2 miscarriages within the last year. Doctors don't have an explanation. I started my period on June 8th, it ended June 14th. My periods are just getting back on track, so that was the first one I've had since my last D&C. I'm not sure if they'll be regular or not. I keep track of my ovulation and fertile days. Today is my ovulation day. The last 2 days have been fertile days. I had sex (unprotected) the day before yesterday an today! I used the bathroom and I had a one time string of bright red blood within my discharge. What can this be? It's not a continuos thing. It was just ONE time. Also, how long does it take for implantation?