Sub-Domain

Hey, I have this question if been trying to get past for sometime now it is to do with Sub-Domains well here it is

I use Enjin.com
My Domain is with CrazyDomains.com.au

I already have 1 sub-domain, but I want another one, do I have to buy a new domain or is there a simple trick to do this. I have different Ips for my servers