It is very tough to temp, it means getting up at the same time consistently 7 days per week.
If you just rely on an OPK, it doesn't confirm that you did O so you can BD all you want and you may not get a BFP (if there is an O issue).
This month I had a doctor monitor my O and I didn't O till about 3 days after my +OPK.
If you are just using OPKs then just make sure that you are BDing for at least 3 days following the +. If you have been trying for a while I definitely suggest BBT.