[cd34]

There is a section in the apache config for your site that probably says:

CustomLog /path/to/access.log common

You want to change common to combined

If in the main apache config you cannot find a definition for combined, or, it complains on restart:

LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-Agent}i\"" combined

is the line that you need somewhere in your config to define combined logging which will show referrers. (Though, apache through the wisdom of an early typo has decided to misspell referrer for years).