Terrible twos???

The last couple of days Brenden has been horrible. He has been kicking, head butting, and even biting. Seriously? What have I gotten myself into? He's throwing wild tantrums and not listening to anything I ask of him. I know this is normal and some days are better than others, but how long does this last. Brenden had one pretty bad day last week, but other than that he's been okay and just throwing little tantrums around dinner time. Does this last a week, a few weeks, the whole year? I just want to prepare myself. Brenden is such a sweet wonderful kid and I want that kid back.