Blocking my own sex scene.....

It probably means directing one's own sex scene.

where specific shots will occur, the angles on the camera, how the actors will lay on the bed or do different positions....all this is done beforehand so the camera person knows how the director wants the scene to be shot. like in soaps, where actors walk from one side of a room to the other, and the camera follows them and then there is a close-up...stuff like that.