conception frustration i fully understand

I'm already a mum of 2 school age children but divorced from their dad about 4 yrs ago. I understand the feeling of wanting to have another child as just recently i have married a man with no children of his own. And so also feel obliged to have a child with him at the start but now i want one just as much as he does and my body seems to be all over the place as when i come on etc so watching my cycle is a nightmare. We have been through so many tests that we could of bought out a whole shop! But we carry on trying but i don't want sex to become a baby making routine as it can cause stress and make it even harder to catch but my partner doesn't understand how a woman can become obsessed with catching even though he goes on about having his little princess which puts more pressure on me then him!