Simply Create a Category and subdomain will be automatically added, so create as many subdomains as you want, you may require one time Configuration of adding Wildcard Subdomain but most of the Host already did it.
Category Subdomain Pro WordPress Plugin Features
- Convert Category into Sub-Domain
- Specifically Exclude Category to be Sub-Domain
- Category Archive page
- Single Post Structure within Sub-Domain
- Generate XML Sitemap for Posts on Subdomain