Designing Kitchens and Bathrooms - Shower head pipe

I have a problem with the short angled pipe that comes out of the wall that the shower head threads on to. When I install it into the fitting in the wall, it stops rotating with the shower head facing the ceiling. I couldn't turn it any further without something breaking. When I turn it back so the shower head faces down, the pipe is very loose and can be moved easily. Not sure if I have a bad fitting in the wall or what but I am concerned with a leak between the pipe and the fitting. The bathroom is finished now and don't have access to the fitting except through the small hole the pipe goes through. Any ideas on how I can tighten this up?

Thanks in advance.

If the fitting you are trying to thread into is an old fitting, use repeated attempts with a nipple to clear the obstruction, install the "shower arm" W/O the head and run the water to clear any debris.

If you've used a thread lubricant such as pipe dope or teflon tape, if not do so.
Liberally wrap the jaws of a pair of channel locks with cheap electrical tape and attempt to turn the "shower arm". If this doesn't work, then remove the "shower arm" and remove a thread from the end of it.You'll need to use a three corner file to straighten the threads, then attempt to use a separate fitting to insure it will thread.