Well, maybe not quite normal, but I have seen that exact same title enough times on this forum to know that it is much more common then you would think.
Do realize that some of this may be due to your new addition coming. I am sure that you probably have not been able to spend as much time with her now as say a year ago. But, ya, this is something that you need to deal with now and not when the new little one is here.
But mainly don't, "spend a large portion of my day saying "the way you are acting is why we aren't (insert whatever activity here)" and she doesn't seem to get that... " Talking to her just will not work. And talking to her when she is having a tantrum - won't work.
The rule is that when she starts a tantrum - she gets a short timeout. And the timeout does not start until the tantrum stops. She will go nuts for a while. Just keep repeating - "as soon as you choose to stop your tantrum, the timeout will start and 2 min later you can ..." Do not try to reason with her or talk with her while she is yelling. You are just playing into her hands.
Essentially, the rules for behavior modification are that there must be immediate, short, consistent consequences. Do not expect overnight miracles. It has taken her awhile to get to this point and it will take a while to relearn control. But she will. A really good book which gets into a lot of detail in using this system is "SOS Help for Parents," by Lynn Clark.
Finally I am providing a link that we did back in January. There are a lot of very good ideas that will help you. Read all of them. While some don't exactly apply to your situation, the answers will.
The link is -
http://www.medhelp.org/posts/Child-Behavior/4-year-old-son/show/2423496
Please post if you have any questions about any of this or the other link provided.