Only hot water coming through bathtub faucet, even when turned to cold, hot water only comes through and on top of that the water runs very slowly.

This morning I have noticed this problem with the bathtub faucet valve. When I turn the valve anti-clockwise from 5 O clock position cold water runs at normal pressure until the valve reaches 12 O colck position. This is usual but when I continue to turn the valve to get hot water the pressure...

The house I live in is old but had all the plumbing redone 2 years ago. I turn the bathtub faucet on and adjust the temp. to my preference but as soon as I turn the handle for the shower head to come on, the water is cold. Majority of the hot water is coming out of the faucet and not the shower...