Problems with internal memory (Sony Xperia M)?

I have a Sony Xperia M (Android 4.1.2) and lately I noticed strange things in my Storage menu in the settings. This is what I noticed:
1. I have absolutely no pictures or videos on my Internal Storage and SD card, but somehow, in the Storage menu, it says pictures and videos take up 368MB (I have 2.05GB total on my phone)
2. This one might not look like much of a problem but it also bothers me: it says I have 708MB free memory, but on the graphic presentation of my memory status shows that I have around 20% free
3. I was going to post a screenshot of this all here, but when I tried to open Internal Storage on my PC (connected with USB cable), nothing appeared in it.

I really don't know what's going on and it worries me.
P.S. I have installed ESET antivirus and scanned my device multiple times (deep scan), but it didn't find any threats.

Additional info that might be useful:
-Apps take up 1.11GB of my internal storage
-Pictures and videos, as said above, seem to take up 368MB
-Audio takes up 112KB (I keep my music on an SD card)
-Misc. Takes up 178MB, which seems to be ok, but I'm not 100% sure as it contains a lot of data which is hard to track and memorize
-The apps I currently have are: Minecraft PE, Warspear Online, Flappy Bird, Chess Free, Google Chrome, Facebook, Twitter, Instagram, Youtube, Steam, Tapatalk, MC Chat, Adobe Reader, AppLock and Eset Antivirus. I'm pretty sure all of these apps are secure, because many people use them and they don't take up a lot of memory (Google Chrome, Facebook and Youtube were already on the phone when I bought it, as you probably know)
-I did have quite a few other apps before this, but I uninstalled them, because I either didn't use them a lot, or they started to take up a lot of memory.

All this is starting to worry me, as I bought the phone about 2 months ago. If anyone knows what it's about, anything that can help is appreciated.

Could be a problem with some app. Factory reset your phone once. If that doesn't fix it, take it to the store.

Just factory reste your cell