i freeze my and cake then frost it and freeze it again, but after taking it out again it starts to melt and looks like its sweating, anyone know why?

It's condensation from going from cold to hot. You can try putting it in the fridge first to thaw.

It's best to freeze in a box, then wrap the box with plastic wrap. If you leave the plastic wrap on while it thaws the condensation should form on the outside of the plastic wrap and not the cake.