Emma
as far as pain relief goes I am afraid the GP and sometimes even your Onccologist are not the best to deal with it. The Macmillan team are excellent they can aso give your Dad a lot of help about tax free benefits he is entitled to that may make it easier for him to slow down a bit at work, Lyn Eyre has mentioned this.
The pain in your Dad's arm could be caused by the hormone treatment and not just bone mets, it seems tht your Dad really needs to see the Oncolgist as soon as possible. Si has mentioned getting onto Zometa or Denusomab and I agree totally, this really helps to strengthen bones and often provides pain relief. Also use of specialised nerve pain meds such as Lyrica can also help.
Opiates can have some bad side effects when taken orally,my Husband had the best reief from intense pain when he was given transdermal patches.
If your Dad is showing signs that he is not responding to the implanted hormone treatment alone (zoladex may be the drug) then another type of daily oral hormone drug is often added something like Casodex (Bicultamide) If this does not bring the PSA and other levels like Testosterone and ALP down then the Onco might suggest Chemotherapy.
There are a lot of different treatments available for a wide range of direct and indirect issues so it might help if your Dad takes you or your Mum (or both of you) along when he has his next consult. If nothing else you will be able to recall what is said so that you can post on here to check things out if necessary.
best wishes
Mo