Mel is is frustrating when your cycles are varying in length. Since charting and i swear this is the reason behind the change (OPK companies are making millions off me!) My cycles have been 40-30-35 and 36 days so i have O at cycle day 26-16-23-22. I usually start around day 12 to be sure that im not missing it.
It sounds like you are doing all the right things, so just keep POAS and hopefully you will get your 2 lines soon.