P.C.
First of all, kudos to you for reaching out for help. You've received some great ideas already, in particular the encouragement to seek professional help. You will help your family the most by helping yourself first. It's important to find a way to relieve your anxieties about your children. As you have already noted, you have started making your 6-year-old anxious when she doesn't need to be. Ask your gynecologist for a referral to some therapists/psychologists, etc. who focus on women's issues and try several until you fid someone you feel comfortable with. If your anxieties are that deep, you may need to take meds, too. That is an OKAY approach; it doesn't mean you are a lesser person. It means that you are strong enough to want to solve your problems and move forward.
All of your children except the baby are old enough to pitch in to help you do some of the household chores. You can turn making dinner into family time by finding ways to involve them, choosing menus, cooking all or part of the menu, just keeping you company and trading stories about what happened today or about what you did when you you were their age -- you get the idea.
You have a lot on your plate with school sports alone. Something may have to give unless you again find a way to involve the others in what you do to make something big. If you can find a way to include them you will be building memories of what they did for each other as well as teaching them skills they can use when they are on their own -- they'll remember to buy or make a card for someone's birthday, or send an ecard without your reminding them. They will be better adults for having helped you. You can even sit down with the older two and talk about how you feel overwhelmed and ask for their input. You might be surprised at their suggestions -- at the very least, they will appreciate your honesty. You can sit separately with your 6-yr-old -- maybe chat while she's getting ready for bed -- just keep it simpler for her. Sharing your feelings will empower her if done calmly, and should reassure you that she's fine without you during the day.
Sounds like you don't like your job, but in today's world, we have to take what we have and make the most of it. Talking about that as part of your therapy might help. Good luck to you -- go quickly and get help.