I actually don't know what my lp is because in previous cycles I wasn't Oing, I think my body was still regulating from coming of bcp. Neither FF or TCOYF could pinpoint O and my temps were ALL over the place. This is the first cycle where both were able to determine O and where I got a positive OPK.
13DPO is really too late for implantation. That said, a lower temp that's still that high above the coverline doesn't mean anything bad. The day I got a BFP for my first DD I had a big drop in temps.
There are SO many things that can cause a drop in temp- something as small as sleeping with your mouth open, or being chillded- so I wouldn't count yourself out just yet.
As of now, it seems that you've done everything right. Good luck!!!!!
BTW- I have to that you were testing as soon as 8-10DPO, but have held out since!! Great willpower!!!!