overly clingy 3 year old

Im about 8 months pregnant with my 3rd daughter and my 3 year old who has always been very independant well behaved kid, all the sudden she turned 3 and all hell broke loose. She turned 3 March 25th and its been like someone swapped my daughter out. She has baby temper tantrums, she wont let anyone console here, anything and everything upsets her, we cant get through an HOUR without her getting upset or being hysterical about something. Shes VERY clingy to me and Im assuming she understands the baby is coming soon, my belly is very big and she sees the stuff being set up and I know it probably freaks her out. She tells me everyday she wants to help with the baby and shes gonna be a great big sister. Then when shes mad she tells me how she doesnt want the baby anymore and she cries and whines about everything.

I try to give her attention and talk to her when she has these fits but she tells me to get away from her and to leave her alone, I want to try and help and Ive been trying to have more 1 on 1 time with her because I see shes having some attention issues. We just feel at a loss, and any advice  would be greatly appreciated :)

While I anticipated the terrible 2's, it seems that 3 was worse in our household as well.  They seem to want to assert some of their independence, but still count on mom and dad for lots of things which causes frustration.  Compound that by the excitement of a new baby, and perhaps a little fear of what is going to happen once the baby does arrive. 

Maybe a little reassurance that she is getting to be a big girl, but she is still mommy's girl and plan something special that only you and she do together, like maybe painting nails or trying a special lipstick on, or sharing breakfast in bed for some girl time. 

Another thing that I would like to add is that when my son turned 3 and started having these tantrums, we found out that he was receiving a juice that contained Splenda at his caregiver's house.  It made him defiant, argumentative and it was almost like he couldn't control his reactions.  He definitely wasn't acting himself and it was more than a 3-year-old's tantrum.  Wouldn't hurt to check her diet and make sure she isn't reacting to something.