Admin SSL Secure Page

I want to secure my /WP-Admin/ login page. I tried define(‘FORCE_SSL_ADMIN’, true); in WP-Config.php and its working fine but after the login my SSL sign giving me “Warning: Contains Unauthenticated Content” message.

I tired Admin SSL plugin but after its activation my WP Subdomains plugin stop functioning and every time browser redirect https://blogs.mydomain.com/post-name to https://www.mydomain.com.

Can anyone please help me how to sort out my this issue.