The "three meals a day, no snacking" does NOT apply to pregnant women or breastfeeding Moms. We need to get our calories in where and when we can, so grazing, snacking, or eating mini-meals is more than acceptible if that's what it takes to get food into your sleep-deprived, feeding-every-three-hours body.
Sipping on a can of coconut milk or snacking on olives throughout the day is a good way to get extra calories in, too. I eat a can of olives pretty much every day. Nuts and seeds are a good calorie-dense source too. I know we say not to crack out on them, but when it comes down to needing to get extra calories in, it's A-OK to rely on these cal-dense sources. Of course, if you find yourself blowing through a jar of Sunbutter every three days, maybe it's time to pull back on that one.
Anytime you breast feed you doing the best you can for your kids. You are providing food that is DESIGNED for them to eat. In addition, they are getting all the immune/antibody benefits that they can get nowhere else. So for those that live in east-nowhere, where the lack of good food is significant, the baby will take from the mother via the breast milk. This happens all the time and it is why the mother gains all the fat that she does to provide lipid rich breast milk to keep those cute little babies slightly ketogenic, which in turn helps their brains grow. But the mom's fat is as good at the nutrition mom eats. So if mom is eating Doritos and McDonalds, that is what the quality of the breast milk will be. If mom is eating real food a la the Whole9, not only is she doing the best she can for herself, but also the baby. At the end of a healthy pregnancy we want a healthy mom, healthy baby and a healthy future. I've been pregnant and I swear Doritos (and their other orange/chip cousins) sing a song, and losing your sanity over Doritos isn't worth it. Have a few if you must, but then get back on the healthy path. Once you clean your system out of junk on a Whole 30, eating non-food will feel like you polluted the system, it is enough of an aversion to not do it again. Your breast feeding kids will tell you the same thing, probably at 3am when you want to sleep!!