Practice, practice, practice
My late wife and I went through 5 years of trying but were finally successful. We had a couple miscarriages along the way. Her body knew enough to adjust for an error in reproduction.
Now, don't let her take this the wrong way.
Years ago, we were raising quarter horses. We already had 3 on the ground. The gestation period is 11 months! So, we breed our mare. Vet check says looks good. The mare is putting on weight. At about 10 months, she is "bagging up", starting to produce milk - a great sign. She is looking really big (fat). Eleven months, get the stall ready and we wait, and wait, and wait. Her teats "wax up" meaning birth is hours or a few days away at most. And we wait and wait and wait.
Finally, we call the vet out. Checks her out - she was never pregnant! WHAT! So what I'm saying, I guess, is the mind is a powerful thing and sometimes you can will your body to believe it.
If it is meant to be, it will happen. Nature has a way of doing the right thing. Relax and things will go as they should.