Hi there M.,
I am a single mom, but unlike you, I only have 2 kids, ages 13 and 7. When it is just one of you, which basically it is, since your husband is working so much, every minute of the day is important.
You must be on a strict schedule,and do better planning. Simple things like getting the kids clothes and bags ready at night, so all they have to do in the morning is get up and get dressed and go. Try getting breakfasts that your kids can eat on the go, like Pop tarts, Fruit cups, Cereal packs, Cereal bars etc. This way, they can eat in the car on the way, if you are running late (or not). Also, putting a load of clothes in the dryer at night, or before you leave in the morning helps keep the laundry from building up. Cook meals on the weekend that will last a few days, and all you have to do is re-heat during the week, this will allow time for other things.
Also, your 12 year old is old enough to handle many responsibilities. If he is not used to doing things, start giving him small tasks first, and then increase them gradually. Even though he is a boy, he can handle things that are Domestic like cleaning, washing dishes, even cooking some things, or at least preparing food without cooking, like making sandwiches. Whatever you choose you MUST utilize the 12 year old. There is no reason why you should be as overwhelmed as you are, with a child of that age. Even your 4 year old can follow simple instructions that will help you out like picking up his toys when he is done playing.
I know it is difficult, because I have been there.
Lastly, you may not want to hear this, but just because your husband is working, doesn't mean that he doesn't have to do ANYTHING in the house to help you. You stated that you are a WORKING mother. Not a Stay at home mom (no offense to stay at home moms). Which means that your children and household responsibilities should be a COMBINED effort. You just have to lay down the law and say "Look, I work just like you do, and I need help!" If your paycheck assists the household financially, he can assist you with the domestic responsisbilities. It is unacceptable for you to feel like a single parent in a two-parent household. ESPECIALLY if you are working too!
I hope this helps. Please don't take offense to the forwardness of this message. My response is merely out of concern, and I am speaking from experience. I am a single mom, AND a working mom, AND I was married once.
Good Luck!
S. P.