I freeze up on top

Sam
I don't no how to say this and it's been bothering me so much, I want to be ontop during sex so so bad but as soon as I get the courage todo it I freeze up and just sit there like a statue, how do I get passed this fear I manage to get on him and then I freeze what do I do? I feel this is the reason our sex life is dwindling because he does do all of the work during sex.