Multiple Calenders

Since updating my 3GS I now appear to have multiple (5) calenders and when syncing all the enteries made since the last sync appear to haev been lost. I have tried to retore from the back up created prior to the last update however this has failed to make any difference. There only appears to be one back up file available in itunes, is this overwritten each time a back up is made, or are the older backups simply hidden somewhere?

I need to be able to merge the current diaries and then reliably sync/back them up as it's the only diary I have.

Help please.