Sounds like you are a signle mom? How old is the kid? He is challenging your authority as children do. You may want to establish a behavior chart based on what he is suppose to do and what you want him to accomplish. Put it on the fridge and utilize it as a rewards system. If he completes the task he gets a check or a sticker or whatever. X number of these equal a reward. If he miss behaves, no check and there should be some sort of "punishment". this can be a time out (NOT IN HIS ROOM WHERE ALL HIS FUCKING TOYS ARE!) or early to bed, no after school special, whatever the fuck you decide. Explain it to him clearly and stay consistent.
If that does not work, a sharp crack on the thigh usually will.
Some times kids act up becuase it gets the attention, do you guys spend positive time together?
Yes, I am a psychologist!