Depending on your installation of Apache, you'll want to look for the ErrorLog directive that is set for the SSL part of your site. This might be someplace like /etc/httpd/conf.d/ssl.conf or it might be in a VirtualHost container for port 443 in one of the config files. Once you've found the ErrorLog directive, see if you see an LogLevel directive around it or in the same scope and either change it to debug or add your own LogLevel directive set to debug. Then restart Apache and now you should get additional error reporting on SSL in the log file referenced by the ErrorLog directive. Of course, as Randolph mentioned, this all depends on if you don't have a firewall blocking the request.
Since you mention that you can make normal HTTPS requests fine (GET) but not your POST request, I think you should also check if you have mod_security running in Apache and try to rule out it being a problem with that.
This link will help you more with the LogLevel directive.