Can you tell me what's wrong my shower water coming down the backof it instead of through the shower head

You have to tighten up the connection at the top.

Either your shower head sits loose in the shower arm or you need new washer. Easy fix. Home Depot "experts" love to help people with this type of problem :-D

First, let's get you more water out of the shower head. Remove the shower head from the chrome shower arm and look inside. You will see a rubber washer with holes around the edge. This is a water saver. Pry it out and toss it. Now wrap three turns of Teflon Tape around the threads of the shower arm and tighten up the shower head. More shower with less leaks now? Regards, Tom