If you just got the positive OPK, then FF won't give you CH until you've got a thermal shift. And, not everybody has a drop in temp before or at O. So, look for the thermal shift and a few days after that you should get your CH. YAY for a positive OPK!!

I hope you got some BDing since the O should happen within like 36 hours of the positive. HTH!! Good Luck!!