A Seven year old is far too young to rationalise, as in, ' if I am nice and polite and do as Mummy says, she will like me more.
Your son is responding with raw emotion to the world as he is experiencing it.
What is happening to you is very hard. Bringing up small children is very demanding and tiring. When we are tired, perhaps we are not as patient as we could be, if we had had lots of sleep etc.
You sound so fed up and exasperated with your DS. You don't sound as though you like him much. ( I am not suggesting that you don't love him) He may not understand why, but he will feel your feelings about him.
If when he talks, you turn away, or you don't smile, or encourage him and you are constantly snappy and are constantly criticising him etc, He will gradually shut down. If he can't get something from you, he may be naughty as at least it is getting a reaction.
There is no way that I am suggesting you are a bad Mother either, because you have posted on Mumnet, so you know that something isn't right. Sometimes we just can't see the wood for the trees.
I know when I was young Mum I got very tired and sometimes I felt like throttling my children and on occasion I did not behave well.
The more miserable I felt the worse my children seemed to behave.
Take some deep breaths, count ten in the face of bad behaviour, praise anything and everything positive that he does, try not to shout or appear aggressive towards him.
Plan nice things to do together and see if your positive efforts over the next two or three weeks make any difference to his behaviour.
He is the child and you are the adult. You are the only one really who can make a difference to this situation.
You also do sound a bit depressed and as though you feel that things are escalating out of your control. So do you think you might be ?
You don't mention any DP or anyone who would help you and the Dcs to have some fun together.
Hugs