More ''other'' data after restoring my iPhone

Hello,

First off, my native languege isn't English so excuse me if I make mistakes. Also, I already searched for other topics on this problem but it didn't help me so I'll just ask it myself.

I have an Iphone 4S (8GB) with iOS 7.1.2 and because my ''other'' data was almost 1.5GB I looked up how to make that number smaller and everyone said that I had to make a back up and then restore it. So, that's what I did. But instead of becoming less, my ''other'' data had become almost 3.2GB and it didn't have enough memory for all the other data (music, photos, etc.).

I've tried to restore it once more and tried to synchronize it several times but nothing changed. So, I deleted all the album artwork, some songs and almost all my apps to try to fit everything on it. Now, my ''other'' data is almost 3GB. It's less but still too much.
Also, when I sync my phone now several songs (around 75) won't show up on my phone even though I do have a little space (around 350MB) left.

Any ideas how can I fix this?

Thank you!