Q: Updating apps from one store when in another country

I am temporarily living in the US, and as such have set up another Apple ID to allow me to purchase apps from the American store, such as retail outlets, health fund banking apps, that are only pertinent to American residents.  I have many apps from the Australian App store which I still use. I have had no problems switching from store to store as required for updates etc.  Two weeks ago whilst trying to update apps on my iPad I was advised that my ID/password were incorrect, (I knew they were not), but changed the password anyway.  I am still unable to access the Australian store on my iPad/iPhone to do any updates.  I can sign into iCloud and the iTunes store using this ID and password on my laptop though. Has anyone else resolved this problem or indeed had the same issues?