No, you do not need to abstain for the whole of the postpartum time! That being said, it is really important to work with an instructor! A book gives you general information, but an instructor can help you in many ways:
-making sure you are making your observations correctly
-teach you how to interpret your chart so you can have confidence in the infertile days, and abstain when you are potentially fertile.
-probably help you identify more days available for intercourse than if you were trying to self-learn the method.
It may be tempting to say,“We’ll just abstain until normal cycles resume”. That is difficult, but possible. However, perhaps if you are able to have another child down the road, that child may be able to be breastfed, and your post-partum infertility may last a lot longer. Also, as you approach menopause, there is likely to be a time where your cycles are not regular that lasts over several years or more. It is really important to be able to use NFP when you are not having regular cycles, and an instructor can help you do that.
I have heard from many people, both on various online forums and in my personal life who learned how to do nfp either on their own or with just a basic marriage-prep presentation. They know very well how to postpone pregnancy when they are having regular cycles, but as soon as something happens where they are no longer having those regular cycles (illness, stress, post-partum, approaching menopause), they feel mainly confusion, and it puts a major strain on the relationship. My experience as an NFP instructor is that couples who love each other will not find it excessively burdensome to abstain when they know that the woman is potentially fertile (if they have a serious reason to postpone pregnancy). However, even loving couples will find it difficult to abstain when they are uncertain about the woman’s state of fertility, especially for prolonged periods of time. They may persevere in their abstinence, which for some couples can bring them closer, but for many couples (especially where one or the other is not fully committed to NFP), it puts a great strain on the relationship. However many couples will end out resorting to immoral means of postponing pregnancy, or they will ‘take chances’ which can result in an unexpected pregnancy. NFP gets the blame, when really it was because they didn’t have help to learn to chart through cycle irregularities.
In your post, you mentioned that it was becoming difficult for you and your husband to abstain. This is not because you don’t love each other, or because you don’t have self-control. It’s because there is uncertainty about whether or not you are actually fertile on any given day, and whether the extended abstinence is necessary. If you knew that you were potentially fertile today, it would make it easier for you and your husband to abstain from intercourse. If you knew that you were not fertile today, you would be able to have relations with your husband, and strengthen your bond, which I’m sure must be being tested by having a child with health concerns.
Please consider taking the time to take an NFP class and have an instructor follow up with you regularly until you return to normal cycles and both you and the instructor feel confident that you know the method. My husband and I teach the Billings method (www.billingslife.org) which is helpful in the post-partum period because you don’t need to take temperature. (Temperature is a less-helpful indicator of potential fertility when the woman is not ovulating regularly, or when a woman’s sleep is interrupted at night). But any of the modern nfp methods are reliable when you work with an instructor during the learning phase, and apply the rules. It will be worth it for you to learn it now, because then it will help you chart through any future time in your life when you are not having regular cycles.