Shape tool dialogue box

Previously when i would select the rectangle shape tool I could click on my document and a box would pop up where I could define the size of the rectangle/square I wanted. This doesn't seem to be working anymore.

Now when I click, a random sized rectangle just appears. When I say random, I mean I didn't chose the size but if I click again the same size rectangle appears again. If I try to click and drag to draw a rectangle, this same rectangle appears and just moves as I drag, rather than enlarging.

Once I have this annoying rectangle I can resize using the free transform tool but it makes the whole thing much more difficult when I need a specific sized shape.

Hoping this is an easy fix as it's really frustrating!