Dear D.,
I am a first time mom with a 1 year old and this was the most difficult aspect of Mothering for me too! I am still working on it, but here are some things that have worked for me. If you don't know how to cook, find someone who knows how to cook healthy food, and ask them to teach you. I took on learning to cook in this first year and I wish I had done it earlier. Anyway, I am learning and it has changed my life.
Buy enough and make enough for leftovers the next day. I have never been big on leftovers, but now that I am cooking they seem to taste better and feel better energetically to me and it is saving me right now. (Ie: instead of making 2 chicken breasts I make 4)
Keep things like cheese and apples, almonds, bananas on hand at all times.
Make soups and use their leftovers. Buy organic salad greens in bulk, make a large container of dressing and use both of them all week.
Create potluck lunches with another mom or two. If it's at your house, keep it simple, like make a pot of whole grains or bake some acorn squash. Easy and nourishing.
During the winter months I have really utilized baking yams, acorn squash, dumpling squash, (which are SOOOO sweet and yummy), baked root vegetables, and slow roasted meats. Having a rice cooker helps A LOT . We just got one recently and I don't know how I did without it. The rice can stay hot for up to 24 hours. Occssionally, I will make double the rice for dinner and then use the leftovers, (which are still hot and delicious he next morning) and make fried rice by adding egg, onions perhaps some ham (ideally from dinner the night before).
One final thing, if I may. I am a Acupuncturist and Herbalist and have spent the last several years studying the importance of diet in our health. I know you know this by now, but don't forget that it is SOOOO important for nursing mom's to eat much more than when pregnant! THis means 3 hearty meals a day plus 2 snacks. It is very important for your health and the health of your baby. If you do not eat enough your baby will need to nurse all the time...trying to get more nutrients. This will still not supply him with enough and will only deplete you further. Also, when you do not eat enough, you will tend to keep the weight on. When you eat a lot of organic, truly healthy food, your body will get back into balance in all aspects much faster. (You actually have to EAT in order to lose weight). It could be that you are nauseous because you are not eating enough in general.
In Chinese Medicine, the Spleen is the organ that transforms food into energy and brain power. When depleted the symptoms are usually nausea, tiredness, lack of appetite, to name just a few. It sounds like your Spleen may be weak and chinese herbs could help this tremendously! Chinese Herbs are very powerful tonics as well, which could also serve to give you more energy to take the task of preparing food on.
Good luck! I totally know where you are coming from (except that I don't have 3 kids!) It's a very difficult part of Mothering and can be overwhelming. But when you start eating more you will feel so much better in ways that you didn't even realize were feeling low.
All the Best,
C.