K.:
CONGRATULATIONS!!
Your son's world has just been rocked - for the last four years he's had all of your attention. Now, he has to share it.
Allow him to touch and explore - he's old enough to understand he could damage or break things - ask him to be careful.
Make a date with him - just him and do something with him - whether it be playing a game in another room without the baby or actually going to the park with him or taking him for ice cream - just the two of you. He needs to know that you still care and love him and see him - that's why all the yelling - he's getting your attention. In his mind, he doesn't care if it's positive or negative, he's getting it that's all that matters to him.
Let him help you with the baby - he can hand you diapers, wipes, etc. if you are breast feeding and pumping, he can stil hold the bottle. He needs time to bond with the baby as well - keeping him away will only build resentment, which could lead to aggression.
Bottom line - let him explore, maybe he can play with the baby when he/she is old enough to use a saucer or playmat. Give him time with just you - schedule it so it's something he will look forward to like a date - it will mean the world to him. Let him help with the baby - let him bond, include him, let him be the big brother and helper.
Everything will work out!
Take care!