It doesn't work if you just put all that left mouse button down code into the left button clicked?
If not for some reason, you could use a variable and use the general condition compare two general values. Use the variable as the first and check if its 0. If it is and the mouse button is pressed, create the object. In the body of the left mouse button is down, set the variable to 1 so its not 0. Then, when you let up the mouse button, set it to 0. That way it only works again when you let off the mouse.