Why are songs on my iPhone deleting themselves?

I have an iPhone 4, my OS is iOS 7.0.4 (latest version), and songs keep randomly deleting themselves, is anyone else having this problem?

More details;

I have PRISM (Deluxe Version) by Katy Perry, and songs keep disappearing from this album (they only disappear from this album), and it gives me the option to download them back from iCloud, which obviously I keep doing, but songs just get deleted again, like I say it's only happening with this album, and the songs that get deleted are all random.

Tonight two had been deleted, so I started to download them from iTunes, a few minutes later I came back to the album to see how they were getting on and two more (different) songs had deleted themselves! It's never ending! Haha!

It's very annoying and would be grateful if anyone could help!

Thank you!

Added (1). I have only used 16GB/28.3GB of storage on my iPhone (32GB one), so I don't think there's a problem with not having enough room for the iOS.

Added (2). I have only used 16GB/28.3GB of storage on my iPhone (32GB one), so I don't think there's a problem with not having enough room for the iOS.

I have an iPhone 4 as well, they're terrible. Basically your phone doesn't have enough space for the ios so it's deleting stuff to make room. Mine does the same but with my contacts. You either need to cut down on music/apps or buy a new phone. Sorry, it sucks but it's true.