Perhaps you are in a develop module tool such as Radial Mask or a tool that uses a Brush where the Oval or Brush size respecively is very small. If you have a scroll wheel on you mouse try rotating it to make the size bigger or see if you have a brush or similar size slider and make it bigger. You can also force a close of any tool bar tools you may have open by (ironically) pressing the "edit" button on the tool bar below the histogram (it an icon with 2 'sliders' on it that just look like horozonal bars.

Not sure what happened but the +cursor is very tiny when over the photo to be worked on, it was larger and more visible a couple of days ago, not sure what I did or how to get it back to normal size.

The extremely small cursor is only on the "edit" page

in the picture

. If I move the mouse to the menus, I will get the normal size of the cursor.
Have you any idea how I can enlarge the cursor size while editing the picture??

Check to see if there is not a cursor size slider in your selected tool

What can happen is the exact opposite. If your brush is set to a very large size, then the boundaries of the brush may be off screen, so you don't see the circle anymore. As a result, you'll only see the small cross in the center of the brush.