I just use Period Tracker app, which I've used since I came off the pill last year just to keep an eye on my cycles and mainly to try to sort out my skin (terrible acne, even at my age! Same as my mother, who still gets it at nearly 70! ), but have started popping down any other changes, including CM changes, from last month. It predicts O date, so trying to keep an eye on that and jump on hubby a bit more near the date (trying to get him to play ball at the moment - he's a bit stressed with new job, and I'm being a mean wife and demanding attention, poor thing!).
If we haven't had any joy in a few months I probably will start doing the odd OPK to see if things are happening in that way as well, but as we are both getting on a bit, we might pop to the doctor if nothing is happening that far down the track (not that 6 months is very long imho, but you know what I mean.....)