J.A.
The best advice I can give you is when he does cry/throw a fit, make sure you state something like "I understand that you are upset about the answer Mommy gave you, but I am not going to change my mind. And your behavior is inappropriate." I know it sounds funny, but it will let him know that you hear him, but that you are the one in charge not the other way around. My neice did the same thing for a long time. The winey voice she talked in drove me nuts. A few weeks of me telling her something to that effect everytime she did it was all it took. I hate to say to kids "stop wining" or "stop crying" because in the long run I think that gives the the negative message of "don't come to me when you're upset".
You might want to try wining back at him so he can see how hard it is to understand you and what it feels like to have someone crying constantly.
I hope this helped.