We're usually out for six months and both my wife and I have issues similar to yours. In my doctors state, narcotics can only be given with a written script and its only good for 30 days. Our solution is to get a few pre written scripts dated 30 days apart, that solves one problem. The other problem is getting the scripts filled in a different state that they were prescribed from. That takes some work, but we've been able to overcome it when necessary. Before I had back surgery, my Dr. would prescribe heavy doses of the pain killer that met the limit for 30 days. This has been sufficient for a 6 months trip.
We use Walgreens, however Walgreens is not in every state. Other alternatives are CVS and Walmart. I use Walgreens for most prescriptions but I use Walmart for muscle relaxers.