I have three kids- my oldest is 9, and I have a newly 3 yo boy and an almost 2 yo boy.
We will have #4 in Dec sometime.
DH is not here. He works away so I am alone 24/7.
Survival techniques matter! If what is happening in your house is not working- change it! Here it helps to have a predictable pattern in the day. When they know what is coming next, there is much less chaos. It felt a little boring to me at first, but the kids thrive on it. Frustrated angry behavior isn't allowed in our home. I'm sure the kids think that rule was made for them- but the reality was that I needed it for me. They escalated as I did. Once I decided I wasn't being the parent I want to be and took steps to change that, their behavior improved- a lot.
I shut down the computer time- particularly for my oldest. Being on it for a bit was fine, but all day was not happening. She balked at first, but after a week it was easier.
EVERYBODY has downtime after lunch in the afternoon. Even the oldest. She can have a book, there is no requirement for sleep, but there WILL be quiet in the house. I will not use that time to clean or do anything 'worklike' . That is time for everyone to recharge- including Mom. It's about 90 minutes long. It took about 2 weeks to get this going reliably, but with persistence on my part (especially with the youngest who fought sleep like craaaaazy) but we got there. If a daycare can manage it, so can a mom.
If the house is a disaster- it's time to purge stuff. There shouldn't be enough stuff in the home to create a disaster in a fairly short time.
Meals are battles- look at why. Change your expectations. Choose not to have the battle- if the kids try to engage in one, be firm and direct, but don't fight. For me, I had to learn to say 'ok'. If a child screams that they hate green beans, I simply put a small spoonful on the plate and say ok. If they eat them, they eat them. If they don't they don't. My job is to offer the food, not to force them to eat it. Dessert here happens once or twice a week- not connected to anything like good behavior or eating their veggies. It just is. The food fights stopped.
Bedtime battles... we've struggled with this lately. Honestly, I set bedtime on a back burner until the days are shorter. They stay up until it is dark, and then we curl up together and read a couple chapters in a chapter book. By the time that is done, they settle down fairly well.
You need to figure out what is overwhelming you- specifically, and decide how to change things so you don't become overwhelmed. You also have to make a conscious effort to choose not to become frustrated and reactive, as it just creates a really messy cycle.
Since your DH is around and you aren't alone, it's time to have a very direct discussion about his helping out.