I totally relate to your post!!
I have a toddler and a teenager both conceived first time trying, we naively thought we could plan the exact month to have the next one. How wrong we were! We've now been trying for almost a year, and find the monthly cycle of hope and then disappointment really really hard and consuming.
Over the past year, we have had one CP and one MMC, but most months nothing at all. We are now trying stimulate IUI cycles through a private clinic to give a helping hand.
Unless there is something specifically wrong that can be treated, then there is little you can do so it's just a matter of keeping trying. People will tell you so much advice about expensive supplement etc, but from all the research I've seen there isn't much evidence that any of it will boost your chances. As long as you're taking a good pre-natal multivitamin and tracking ovulation then there's not much else to do.
There is some evidence taking CQ10 supplement can help, so we do that too. And I recently brought the Pre-Seed lubricant and Ferti-lily cup to try out - again just to give us the helping hand - nothing is guaranteed despite what they advertise on the box, lol!
End of the day, it's all so random isn't it. Heard many stories of ppl doing years of fertility treatment and then accidentally falling pregnant. And then people who get pregnant easily and then can't ever have another.
Some useful resources other people on this site shared with me which I found helpful - Robert Winston's website - reading all the Q&As on fertility, also a video called "the great sperm race" it help to get perspective on why conception is actually quite difficult.