When I pull the rod up now, virtually no water goes to the shower head, this is so simple, the metal rod and the plastic piece it is attahced to, what can have gone wrong with it?

It is a simple matter of the plastic not sealing where is meets the metal and does not send the water up to the shower head. I suggest that you buy a new tub spoud just like the one that you have and replace the old one.

It is a fairly simple job to undertake.