A.,
I'm sure you've heard of "the terrible twos"? Well, he's getting there! :-)
Your first mistake is allowing him to watch TV when he gets up that early, or when he throws a tantrum. I know that you're probably tired and worn out, but you don't reward naughty behavior. Also, if he's like most toddlers that age, watching TV is probably very stimulating to him, and is not a good way to get him back to bed!
It sounds as though he's screaming just to get his own way, or to get your undivided attention, which you shouldn't allow, just because he's crying. If you don't get this under control before you have your new baby (congratulations, by the way!), you're going to lose your mind! LOL
When he gets up that early, I would go to him, give him a hug, and tell him that you love him, but then explain that Mommy's tired, and that you need him to go back to sleep for awhile. Put him back in his crib, and close the door. If he screams, wait 5 minutes, and then go into his room, and again tell him he must go back to sleep, or at least lay there quietly, until it is time to get up, then leave the room. If he continues to scream, wait 5 minutes and go in again, but this time simply let him see that you're there, without talking to him, and then leave the room. Continue to do this at 5 minutes intervals, until he goes back to sleep.
The next day, do the same thing, but only go into his room at 10 minute intervals, and the next day wait 15 minutes. In this way you're reasssuring him that you love him, and that you're there for him, but that he must stay in his bed, and allow you some time to yourself.
You can also do this when he refuses to allow you time for yourself to sit down, or be on the computer. Explain that he needs to play with his toys, while you play with yours. If his naughty behavior continues, then put him back in his crib for a "time out". He's still very young, so 5 minutes is a good time out. Then let him come back out with you. Then you can allow him some TV time. However,If he goes back to bothering you, then the TV goes off,and he gets another 5 minute time out. If you stick to your guns and be consistant, sooner or later, he will understand, and you'll have a much better behaved little boy.
This is going to take some work on your part, and listening to him cry will be very hard for you, but you need to put a stop to this behavior before the new baby comes. He has to realize that there is more in your world than just him, or he may be terribly jealous of the new baby. If you can get this point across to him now, it will be much easier for him later on, when he has a new sister or brother to share you with.
Remember, letting him cry will hurt you much more than it will hurt him, and is for his own good. (Investing in a good pair of ear plugs may help, since you're going to have to "out stubborn" him to get your point across!)
If its any consolation, many toddlers go through this once they approach 2 years old, and you just have to be consistant with your discipline until it sinks in!