Jody, I know exactly what you are going through. My 3 year old is the same some days, and it means that you get very little done. It is sooo easy to get stressed out, and the more stressed out you get, the more out of hand the kids get, and so it goes round.
The trick that has worked for me over the years (my eldest is 16), is a) try to be totally calm and relaxed yourself(not easy I know - it will take practice).
B) Be consistent with whatever discipline that you choose, and whatever rules that are incorporated into your routine eg: child has to make his bed everyday - make sure that it actually gets done.
c)Relax your own strict code. I used to panic about the house being perfect, now I don't worry if things are not done 100% or things get a little untidy. I would rather spend time with my kids, knowing as I do that they are here for such a short time. I will have all the time in the world to clean etc, when they are all grown up.
Good luck with it. Just remember that kids don't come with a set of instructions, and what works one day often won't work the next. It also helps if you have someone in the same boat to talk to. Have you maybe tried the local playgroup? I often found that after I had been there I felt that my kids were the best of the bunch