He doesn't like pressure to perform

I'm 36 and my partner is 39 and we're TTC for our 1st. We've been trying about 8 months now, very casually at first but the last few months I've started using OPKs, tracking my BBT and it's definitely on my mind a lot more than when we first started out. My problem is that my partner doesn't like the pressure of having to have sex on my ovulation days and says it should be more natural not forced. Unfortunately as we both work shifts we can easily go a week at a time without sex and I want to maximise our chances at peak times. Does anyone have any tips or advice or are experiencing the same problem with a reluctant partner?! He says he wants to start a family with me but I don't understand why he doesn't want to put himself out to achieve it. Sorry for the rant it's just really getting me down. x