How can you tell what gender you are mentally?

I am suffering a crisis of identity. I keep wanting to engage in activities of the opposite gender and I like it a lot, Is this normal? Should I do something about it? Its like half of me is represent in being male and the other half being female. I feel i need both sides to be me, but I can reign either side into one gender. I am a very confused person. So what do? Also i posted this question twice to get more answers.