We're dealing with this too.
I try to get her outside every day, it helps her mood alot.
I have a list of things for her to do, if she's acting up I don't have to think about it too much and just get her started on *something* LOL.
- blowing bubbles outside
- crayons and painting on the back deck
- read a story
- let her loose in one of the kitchen cupboards
- let her loose upstairs (she doesn't get up there much except to sleep)
- singing and dancing (Hi 5 and we do the singing and dancing tog.)

I think it's a combination of boredom and not being able to communicate the way she wants (she's not talking much yet, but getting better).
We live in a townhouse - very confined so some days you just want to tear your hair out when it starts