Why is it so hard to get pregnant when im planning? But so easy when i wasnt???

Any other ladies have this? I had two unplanned pregnancies before being married (did marry their father later, we wanted to wait) and now that we have been planning and trying for 10 months its not happening :( we had a miscarriage last year and haven't been able to conceive since. Its a bummer and gets me down. But its gotta happen sooner or later right? I just can believe it was so easy when I wasn't planning and so difficult now that I am planning.