Typing in my subdomain automatically redirects to my main URL. I am almost positive it is something in my .htaccess file that forces the redirect. I had a lot of trouble setting my site to only use https://, so I think that may be the cause. I created both an A record and CNAME record for the subdomain. I am making a documentation subdomain for my website, (docs.example.com).

My .htaccess file contains the following:

<IfModule mod_rewrite.c>
RewriteEngine on
RewriteCond %{HTTPS} !=on [NC]
RewriteRule ^(.*)$ https://%{HTTP_HOST}%/$1 [R=301,L]
RewriteCond %{HTTP_HOST} ^www\. [NC]
RewriteRule ^(.*)$ https://[my website url is here].com/$1 [L,R=301]
</IfModule>
# BEGIN rlrssslReallySimpleSSL rsssl_version[3.3.1]
<IfModule mod_rewrite.c>
RewriteEngine on
RewriteCond %{HTTPS} !=on [NC]
RewriteRule ^(.*)$ https://%{HTTP_HOST}/$1 [R=301,L]
</IfModule>
# END rlrssslReallySimpleSSL

# BEGIN Really_Simple_SSL_SECURITY_HEADERS
<IfModule mod_headers.c>
Header always set Strict-Transport-Security: "max-age=31536000"
Header always set X-XSS-Protection "1; mode=block"
Header always set X-Content-Type-Options "nosniff"
Header always set Referrer-Policy: "no-referrer-when-downgrade"
</IfModule>
# END Really_Simple_SSL_SECURITY_HEADERS
# BEGIN WordPress
# The directives (lines) between `BEGIN WordPress` and `END WordPress` are
# dynamically generated, and should only be modified via WordPress filters.
# Any changes to the directives between these markers will be overwritten.
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress
# Wordfence WAF
<IfModule mod_php5.c>
    php_value auto_prepend_file '/var/www/html/wordfence-waf.php'
</IfModule>
<IfModule mod_php7.c>
    php_value auto_prepend_file '/var/www/html/wordfence-waf.php'
</IfModule>
<Files ".user.ini">
<IfModule mod_authz_core.c>
    Require all denied
</IfModule>
<IfModule !mod_authz_core.c>
    Order deny,allow
    Deny from all
</IfModule>
</Files>
# END Wordfence WAF

Also, do I need to configure an SSL cert for my subdomain or will my other cert cover it? Thanks!