Why does my iPhone calendar keep deleting events every time I sync?

I have iPhone 4S iOS6, and every time I sync, my events that I have made on my phone disappear completely. My calendar is not synced to anything either (for example Outlook/Gmail) It's only synced to my Hotmail calendar because I've synced my email address with my Mail app. And I'm not sure if this affects it, but I've also synced my contacts with my Gmail account too.

It's not because I haven't selected "All Events" either.

Please help me, I am getting incredibly irritated by this!

Thank you.