IPhone 4: no memory left but I barely have music or photos on my phone?

I have an iPhone 4, had it for almost a year now.
I barely have ANY photos, BARELY any music.
and my camera/app store/voice memos are always telling me I need to delete stuff because there's no more memory.

6.3 GB Used
55. 8 MB available

Now. I guess I should briefly explain how much stuff I have on this phone.

123 photos. 0 videos.
Nothing in photo stream, I delete what's in that.don't need it.
Also no other albums just the main one.
11 apps. All I NEED. I've deleted ones that aren't needed to obviously save more memory.
168 song. Yup all I listen to.

7 voice memo recordings (around 15mins added up)

9 quite long notes…

MUSIC: 930 MB
PHOTOS AND CAMERA: 530 MB
Other apps estimate around--
61, 48, 42. 39… (So on)

Like I'm not sure what the problem is. Is this just the consequence of having a low number of GB?
I can barely take photos at all!
Could this be maybe texts? Call log? Emails?( I never use it, yes it is always piling up)
Open apps?(double click)

I use Facebook, and twitter in safari to save memory too. Freaking sucks
I know this question is extremely long…
If you've read this far, thanks so much. Please give me an answer! Maybe this is all my GB can hold I guess… Haha

It's difficult to say what is taking up the space without looking at the handset.

Pop into your local Apple store, they'll take a look for you.