SGS4 can no longer write to SD card?! Help!!!

[AC Question]

Ever since upgrading my SGS4 Lollipop form KitKat, I haven't been able to add new files to my SD card. This means that I can't save songs on Spotify, can't take any new pics and save them, nor can I download new apps that are too large to be saved to device storage. This has really screwed me over. I'm going travelling for about 9 months, starting in 2 weeks and I really need to be able to take pics and download new music. Any help on how to sort this problem out would be very much appreciated!