I just bought a SD card for my Samsung Galaxy S5 and its still showing storage space running out. The Sprint store said it takes a few days for it to go away?
This is quite normal, especially if you've recently inserted the MicroSD card into your Android device. What you can do is go into
Storage and change your default location for installed applications and files.
Did you migrate your files?
So, I'd assume that the files on your phone is what's taking up your storage. What you can do is install something like ES File Explorer. It has something like an SD Card Analyst built in and lets you copy all of the files from your phone to your SD card (or vice versa). I don't know, but I'd image since you got an SD card, you haven't yet configured all of your files on it. I'll update my answer with more advice, provided you update your question or make a comment asking for further help. Good luck!