You've gotten some great responses from the others, so I'll just say that I agree with what they say and then add one more thought. The others have already mentioned developing a daily/weekly/monthly plan to handle the things you do regularly. This includes things like housework and grocery shopping and running errands. The more you can create a system for these things, the less you have to think about them and waste time trying to "fit them in."
You also mentioned that you are committed to your business, and I think that is *key*!!! That belief in yourself and your business will start opening some doors for you that wouldn't exist if you were still on the fence about whether you really want/need/can do this job.
So the thing I wanted to recommend is very simple: Set boundaries. All over the place. You have to be the one that creates them so that your husband, children, friends, neighbors, family know that you are unavailable. Set a schedule of your work hours. Get the mother's helper or the sitter to come in. Have your husband take over from 6-8:30pm. There are many options, but it sounds like so far you haven't delineated any time to commit to your work hours.
I've been a WAHM for three years and I have three children under six. My coach had me do several things that made me set myself up for success in my business. The first was to commit to it. The second was to get buy-in from my husband and family, since it affects them. The others were to create an office space, to set regular office hours (and keep them) every week (sometimes this was only three hours a week, but I did it regularly), then to open a business checking account, and to set aside money for my expenses in a business savings account (use this for the sitter, home office expenses, etc.).
What I realized and what I have seen in my friends and clients many times is that we as mothers don't often take our businesses very seriously at first. We do it only when we can steal a minute when the kids are sleeping or watching tv. Or after we've done all the other things we are responsible for (without asking for help or delegating some of it, like housework and errands), and we do it on the couch or in the car or with a baby on our laps.
I'm not saying that any of this is wrong, but it eventually leads to a lot of frustration and resentment for everyone. If you set up some clear boundaries and some expectations for your clients, family, etc., then everyone will know when you are available and when you are unavailable. Have your sitter or mother's helper keep the kids away from you during your work hours. Perhaps first you have to give yourself permission to take this time for yourself or for your business. It's hard, I know! I spent the first three years of my motherhood feeling like it was wrong to leave my kids with a sitter or to even not be available when they needed/wanted me. In short, I had no boundaries and was just struggling to be everything to everyone.
I love my work. My business is a source of immense fulfillment for me, and my family understands and supports this. My older children know that I'm off-limits during office hours, when the sitter is here, and they understand when I give them the kitchen timer and say "I need to do some work for 15 minutes. When the bell rings, you can come and get me" when the sitter isn't here. And I quit when the bell rings. That way they know I'll be there for them.
And as I write this, my two boys are begging me to do something since they're bored, so I got a bit long-winded and rambled, but I hope this helps you!
To your success!