you overreached and now you're burnt out, just like you said. you have to be realistic.
it doesn't have to be processed foods, and it doesn't have to be every single thing organic and home made, either.
a typical day at our house- cereal and milk for breakfast. carrots and peanut butter for a snack. a sandwich, apple slices, and some wheat crackers for lunch. home made popcorn for an afternoon snack. dinner might be something easy like shrimp and grits with green beans, or meatloaf, or homemade hamburgers and sweet potato fries.
it does NOT have to be expensive or complicated to eat better. and you can't shield him from everything. as a child grows up he will become exposed to more and more of the "real" world. it's better to teach him moderation and healthy alternatives, than to try to "protect" him from every little thing. teaching him will serve him better in the long run as he grows to adulthood.
decide where your boundaries are (for food as well as behavior) and STICK TO THEM. pick realistic goals. for example: goal #1 might be "no more chocolate milk at restaurants". we are a water family. occasionally my husband will get sweet tea, but we don't drink sodas and my son will usually order water as well - occasionally will ask for milk. that is a biggie with me. humans don't need milk past the baby stage. water. we don't even do juice - like you said, too much sugar. (drinking anything other than water is the quickest and easiest way to fill your body full of unnecessary calories, fat, sugar, sodium, etc)
go back to the basics on discipline, do your time outs consistently and if you lay down the law at home he will see you mean business. it may not be wrinkle-free in public but you will have to devote your energies to that, rather than home-made organic foods. you can't do it all. i'd rather make a few small compromises and have a beautifully behaved, healthy, stable child. hang in there.
(take lots of notes if that helps. write down where you are at, where you want to go, what you need to work on...it can be overwhelming. take one step at a time.)
i don't understand why, but no one ever seems to tell us that parenting IS HARD WORK. it really is. it's not for sissies. and you can do it just like the rest of us can do it. hang in there!
ETA: the moms have a good point. you really do need time for you at some point - after that first year or two we all start feeling it. it's too much. we can tell you but you really probably already know - a stressed out, defeated, overwhelmed mom is not a good mom. so fix you too! send him to grandmas for a weekend, whatever you need to do. hang in there. you can do it.