I've known very overweight women, and very skinny women who had no problem carrying multiple healthy pregnancies to term; and I've known 'average' weight women who simply couldn't get pregnant, regardless of how much lettuce, almonds or red grapes they ate.
Does it help to eat a healthy diet and to exercise appropriately? Probably, yes. Is that the only factor involved? Definitely not.
And spiritually, it's the same story, too. I've known people who prayed very little, who got answered ASAP. I've known others who did multiple prayer sessions at Kivrei Tzadikim; 40 days at the Kotel; 90 days in a row; six hour mega sessions - and nothing. Or at least, nothing obvious, as no prayer ever truly goes to waste.
Some people keep no mitzvahs - and get pregnant at the drop of the hat. Others keep lots of mitzvahs - and a decade later, still no pitter patter of little feet.
The point here is that G-d, and only G-d, decides who gets pregnant, and which souls are going to come down to the world.
But having said that, there are a few things you can do to clean up as many 'blockages' as you can in the meantime, because infertility often comes just to teach a lesson, or create a fundamental change, and once that happens, many people can then go on to become parents.
The following is not an exhaustive list, and I'm not pretending to be the world's expert. These are just my learnings about infertility, gathered the hard way over the last few years. If you do the following, you'll definitely maximise your chances of getting pregnant, and delivering a spiritually and physically healthy child, if that's G-d's plan for you.
1) Keep the laws of family purity - ie, go to the mikva every month after you've counted seven clean days from the end of your period, and do at least three bedikot - the first and last ones, plus one in the middle. Children who are born in spiritual purity have a much easier time of it in this world, and are much calmer, happier and healthier than otherwise.
2) Get your ketuba checked. If you're keeping mitzvoth but aren't having children, this is the first thing to do. The ketuba is your marital 'DNA'; if there are errors in your ketuba, it can potentially cause lots of problems. (Rebbe Ashlag, in Bnei Brak, is highly recommended. You can schedule an appointment by calling the office number: XXX)
3) Eat as healthy as you can, and cut out the cigarettes, alcohol and diet coke. (Diet coke may even be the most dangerous thing in this list…)
4) Pray for G-d to give you healthy children - and then forget about it and try to enjoy your life as much as possible. Don't spend all your life 'waiting to concieve', as that will crush your spirit like nothing else, if it doesn't happen.
5) Strengthen your spleen, kidney and liver meridians - these are the three 'yin' meridians that most affect conception, hormones and everything else related to the female body. If these three meridians are strong, it means your body should be operating efficiently in these areas.
6) Go visit Rebbe Nachman - there are so many miracle stories about people who tried everything, for decades, who got pregnant after a trip to Uman. Don't wait 20 years and then do it in desperation; go as early as you can. There's no rule that says miracles only happen after a 15 year wait.
7) Work on your happiness and gratitude, and don't blame yourself for anything. These three can be SO hard for a couple who are struggling to conceive, and particularly for the woman. Infertility is a test of emuna unlike nothing else, especially when the time of the month rolls around again. But energetically, happy energy and gratitude strengthen a Radiant Circuit called the 'Penetrating Flow', which is crucial for conception.
Spiritually, happiness and gratitude enables you to enjoy your life even while you're waiting for the kids to show up.
And emuna-wise, nothing sweetens the harsh decree of infertility on a person as fast or as effectively as being grateful to G-d, and happy with your lot. But this is serious work, and a very high level of emuna, so DON'T BLAME YOURSELF if you still get down and depressed, particularly around the time of the month.
G-d understands it's not easy, but He still wants us to make the effort.
B'hatslacha! And may you be blessed with healthy, happy babies very soon.