Has anything happened at Pre school or nursery that has disturbed him? Also check with your GP that he hasn't got any infections ( ear problems)
Then, if all is clear, you need to consider that this is fairly normal behaviour for a four year old. They do push the boundaries and they do become horribly contrary. They also know they can behave like this with you as you will always be there for them.
If he hits you again, I would get down to his level and say with a stern face how absolutely unacceptable this is, and how hurt Mummy is. Try to be patient and consistent when you withdraw rewards for bad behaviour. Try and concentrate on the positives.
He is hardly past being a baby and is just not capable of plotting to make your life miserable.
I used to use distraction a lot.
Me.... Come and put your coat on.
Child.... No I don't want to!
Me ...( turning my back to the little rogue) Oh! Look at this,! pretending I could see something out of the window.
Child.....comes over to see what I could see, allowing me to get hold of him and slip his arm into the coat as I said..... There was a large big, huge bird/ space ship/ Darth Vada out there....etc etc...
You have one go at bringing your DCs up to believe in themselves and respect you. They deserve to be treated like you would like to be treated.....that is with patience and respect.
We have all been there, believe me, and feel like throttling the little so and so's, but if you can count ten and be as patient and as loving as possible, you will be rewarded in shedloads when they grow up.
They won't remember your exact words but they will remember the warmth and love they received from you. I remember my childhood, as I received none.
hugs, because we have all been there, and it is not easy having DCs.