Agree with the immediate steps being: (1) breathe; (2) emergency fund; (3) changing your withholding; and (4) checking into your child support/alimony rights. Do not let the desire to be the good guy deprive your child of assets that s/he needs and you have every right to. You are not being a bitch if you nicely and politely require him to pay what the state says he is legally required to.
As you have a little head space, other things to think about:
1. Try YNAB or some other tracking software. Given the very few budget categories you listed, I suspect there is other stuff floating around you didn't think about (car maintenance? Netflix? Co-pays? Bank fees? Etc.). It will be very helpful for you to really see where your money is going so you can plan appropriately.
2. Really re-think your insurance, because you are paying money you don't have for an illusion. Worried about running into someone with a Mercedes? Guess what -- you have no assets for them to go after and are low-income. This is what is known in the legal profession as "judgment-proof" -- it's just not worth going after you, because it will cost more to do that than they could ever collect. And that means that even if you get sued and it's your fault, the Mercedes driver will very likely have to settle for the limits of your policy -- even if those limits are low.* This is a cart-before-horse thing: increase your insurance after you have assets to protect!!
And on the flip side: worried about someone running into you and totaling your car? Guess what: their insurance pays for that, not you! So keep comprehensive (that's the "I hit a deer" coverage), and make sure the uninsured motorist coverage is high enough to replace your car if needed (that's what would pay if it's their fault and they didn't have insurance -- but for a 8-yr-old Prius with 200K+ miles, that can't be more than a few thousand dollars anyway), and cut everything else to the bone. Also, ask if your insurance company has any "safe driver" discounts -- I know our insurer will give a pretty significant discount if you put a tracker in your car and drive safely. You are very likely stuck with massively high insurance because your credit score is so low, which puts you in a category of people insurers think make more claims. So do whatever you can to show them that that's not you.
3. Focus on making sure your transportation is covered. This means extra set aside for repairs and for a replacement vehicle. You are much more likely to find yourself without transportation because your 200K-mile car broke down than because someone hit you -- and yet you are paying $200/mo to cover the latter, and have absolutely nothing -- nada, zero, zilch -- to cover the former. After your minimal EF, this is really a top priority, since losing the transportation likely means losing the job and your only source of income. Also, be creative in looking for options that you might be able to use for the short-term (buses, a bike, a moped, even Uber once in a while) so that if your car does break down unexpectedly, you at least have a backup plan at the ready.
4. When you have the head space, look into the collections account. I am a little worried that they are likely charging very high interest and monthly fees -- one of the tricks they do is to charge a "late" fee each month, even if you are making regular payments, because the old accounts are still technically late (because, duh, they went to collections). Before you decide whether to declare bankruptcy or what debt to prioritize, you need to understand what this debt is actually costing you -- if they are charging 20% interest and $200/mo. in fees, for example, that makes it almost impossible to get out of, which would argue for either bankruptcy or throwing every penny at it ASAP. This is going to be tough for you to do, because it will be scary numbers, so find a friend or someone you trust to sit with you and help you through it. Also, were you hurt while you were married or after the divorce? If it happened while you were married, that is something else that your husband should be somewhat responsible for helping with, since he was the family breadwinner at the time, so that's something else to talk to a lawyer about.
Finally, if you do declare bankruptcy, that will involve several thousand dollars in legal costs, so you will need a contingency plan to save that up (many bankruptcy lawyers want their money up front, which shouldn't be surprising if you think about it).
You can do this! FWIW, my mom was also a single mom for a good part of my childhood, making a low income, on food stamps, etc. We made it through with frugal living, she got her degree, and @40 years later, she is a multi-millionaire, and I have a college and a professional degree and am FI and could RE any time I want. This is a temporary blip, not a life sentence for you or your kid.
*Secret lawyer knowledge: in many states, there is a rule that if the accident victim offers to settle for the maximum limits of the policy, and your insurer turns down the offer and then loses in court, your insurer has to pay the entire amount of the judgment -- even if it is beyond your policy limits! This is one reason most accident cases settle for whatever the policy limits are.
