Phone memory trouble?

[R]

I have a Samsung galaxy and a 32 gigabyte memory card, but my phone is saying memory is full and sometimes SD card is full. I highly doubt that all my memory is used up. Even when didnt have any apps on my SD card it still said it was full. I doubt that photos or anything else would take up that much memory. And my phone said that there was 20 something free gigabytes of memory so something is wrong. It won't let me look at myphotos by going to the gallery and I can't upload anything to instagram. I used to be able to just uninstall apps and it would work but that doesn't work anymore but even if it did it still is a problem because I should have more memory. Please help