3 yrs olds

I'm having a hard time adjusting to the 3yr old stage. When one minute everything is fine and then in a blink of an eye the world has been turned upside down. How do you get a 3yr old to listen to you? I have tried many different things and so far nothing has worked. Night time is the hardest, but I just take it one day at a time and hope for the best the next day. I know it is just a stage and he will hopefully grow out of the screaming and hitting soon :) Cooper has also been off his game a little. Not sleeping and he LOVES to sleep.  Hoping its just a tooth coming in and not much more. Hes crying again so im off to calm him down. The life of a mommy :)