Hm ... I know my temps are REALLY erratic in the beginning of a cycle ... huge dips and rises ... so I get crosshairs at least twice before I actually O. So I am really big on interpreting my charts myself.
I think CD 17 also looks good for O. That would explain the signs yesterday and there might be a nice gradual temp rise in your future instead of a SHARP drop and rise. More like what happened after CD 7. If your temps keep going up like that it might be worth considering CD 17 to be O instead of 13 even though that would be the same pattern twice.
FF says you're sick? Could you have had a low fever on CD 4/5/6 before realizing you were sick? That would make CD 13 look a LOT less like O.
Maybe you were gearing up to O on 7 and it didn't happen. If all the other signs point to O more recently, that's a possibility. So consider all the signs and not just temp.
Is that clear enough? Yeah, I know ... clear as mud, right?