I had to laugh out loud at the person who suggested the OP certainly could not be doing it right since he and his wife had 4 kids in 5 years. We had 5 in 5 years! And yes, I exclusively breastfed all of them. In fact, I nursed right up until the next one was born in several cases. My periods returned anywhere from 6 weeks to 3 mos postpartum, despite nursing AROUND the clock. So much for LAM! I NEVER offered a bottle before 6 mos. We did not even use a pacifier for our first 3. Our 3rd was a 25 week preemie, so that does make the spacing a bit closer than it should have been. (3 kids in 27 mos should not be physically possible…but it was!). But suffice it to say, I now have a 7yo, a 5 1/2yo, a 4 1/2 yo, a 3 1/2yo, and a 20mos. And I am sure #6 will be conceived soon. My OB begged us to give my body a break. I have several health issues that arise during pregnancy, making the pregnancies difficult and high risk. However, he knows that we will never do anything to take God out of the picture. We have been abstaining during my fertile periods for the past 20 mos since we delivered our “baby” but we have now decided it has been enough of a break and we are feeling the call to be open to more.
As for the OP, my only advice is to continue to pray. I understand your feelings that NFP has “failed” you. My last 3 were conceived during what I was CERTAIN were safe times. I followed the rules, we waited until after the 3rd dry day, and then had intercourse. However, it seems that I had not already ovulated as we thought, or maybe I ovulated again…who knows. Regardless, I now have 5 children, 4 of whom certainly were not “planned” but could not be more loved or wanted had they been planned. In fact, I look at my kids and think back to our “plans” of having 1 every 2-3 years, and I wonder which one(s) we would not have right now. I can’t imagine my life without any of them. That is what led us to throw away “our plans” and live by God’s plans. He alone knows what is best for our family, and we trust fully in Him to provide for us. No, it is not always easy. I will be the first to admit that there have been many days where I cry myself to sleep. Days that I scream at my kids because I am simply at the end of my rope. But I continue to pray for the grace to parent well. My mantra is, “God, you blessed us with these precious children. Now, please bless ME with the grace I need to be a mother worthy of making you proud.” I have found that this simple prayer works wonders. I am much calmer now than I was when I only had 3. I have much more patience. Yes, I still have bad days…who among us does not? But if you had asked me 3 years ago if I would have been considering a number 6, I would have laughed in your face. It is amazing the blessings and graces you will receive when you fully submit to God. So please, do not give up yet. God is not finished with you. He may not have more kids planned for you, but my contracepting, you are completely shutting Him out. Spend some time in front of the Blessed Sacrament. Pray. Go to confession. Pray some more. Most importantly, trust in God.