Files on SD not showing

[Mellowstep]

I'm having issues with my SD in my Lenovo Tablet. I restarted it last night and, when looking at it this morning to find a photo, noticed that all of my media was gone. All my photos, music, videos, even the Gameboy Advanced ROMs I had downloaded. None of my apps (i.e. Facebook or WhatsApp) show any files when I try to send a photo from my gallery. When I connect the phone to my pc, it shows a large portion of my SD is full, which is the same amount I remember it being full by last night. I'm not really good with computers, tablets or phone, but I (with advise from a friend who knows way more than me) have tried the following:

• restarting my phone again
• taking out my SD and putting it back in
• running a data-recovery from my pc (the program refused to let me select the SD as the thing I wanted to recover data on, so that was a bust)
• checking every single folder in case it got moved around due to an update
• showing hidden files on my tablet itself, which didn't reveal anything
• running a full anti-virus with my phone's anti-virus program (it found no problems, but scanned over 2500 files, which is way too many to just be system files)
• downloading a new file manager and disabling/deleting the one that came with my phone
• deleting the new apps I downloaded last night in fear that it was messing with some settings

I got the phone on the 30 January 2018, so it's still brand new. It's had a small issue where sometimes it won't let me delete or save files, but that was always fixed by rebooting the phone (which is why I restarted it last night). At this point, I am out of ideas and out of options. Any help would be appreciated greatly.