iCloud wont back up my iphone 4s

Hi

My iPhone 4s won't back up to iCloud.

When i look on the settings>icloud>storage&backup>manage storage>my iPhone, it says under back up options that my next back up size is 5.4GB. This is obviously too large for the free 5GB back up i have. The main culprit for this is camera roll. It says that the next back up size would be 5.2GB for the camera roll.

So i have deleted loads of videos and photos and my actual camera roll storage at present is 1.8GB (settings>general>usage>storage)

Cant understand why this reduced amount is not recognised by iCloud when trying to back up.

I have updated to the latest softwear ios 6.1.2 but this has not fixed (or caused) the issue

Any help much appreciated

Thanks