.htaccess intrupting add on domains on shared hostin - apache

Question

This is the code in my .htaccess file which is in the root directory of my shared hosting.
RewriteEngine On
RewriteCond %{HTTP_HOST} !^www\.
RewriteRule ^(.*)$ http://www.%{HTTP_HOST}/$1 [R=301,L]
RewriteCond %{REQUEST_FILENAME}!-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^([a-zA-Z0-9\-]+)?$ interest.php?interest=$1 [QSA,L]
RewriteRule ^([a-zA-Z0-9\_\-]+)?/$ interest.php?interest=$1 [QSA,L]
The problem is, In the same directory lies folders of my add on domains. When I am trying to access them, the 2nd line is creating problem and redirecting it to my primary domain. I want the .htaccess to effect only root folder and not its sub folders. I tried reading other similar questions here and tried changing my htaccess accordingly but the problem remained unresolved.
For example.
its redirecting
mysubdomain.mydomain.com
to
www.mydomain.com/mysubdomainfolder

Answer 1

Have your first rule like this:
RewriteCond %{HTTP_HOST} ^mydomain\.com$ [NC]
RewriteRule ^ http://www.%{HTTP_HOST}%{REQUEST_URI} [R=301,L]
Then clear your browser cache and restart your browser.

Answer 2

Well, .htaccess files are designed to apply recursively.
You could try putting a .htaccess in each of the subfolders that correspond to your add on domains with RewriteEngine Off if you want no redirects, or an alternate rewrite rule if you need them.
In addition you may want to add another rewrite condition for the rule, say your add on domain is blah.com you could add
RewriteCond %{HTTP_HOST} !^(.*.)?blah.com
Edit: I should add the new rewrite condition should go below RewriteCond %{HTTP_HOST} !^www.
Edit2: Okay so subdomains then. In which case you basically need to add a Rewrite condition specifying not to apply the rewrite rule if it's a known subdomain. For example:
RewriteEngine On
RewriteCond %{HTTP_HOST} !^www\.
RewriteCond %{HTTP_HOST} !^(subdomain1|subdomain2|subdomain3)\.domain\.com
RewriteRule ^(.*)$ http://www.%{HTTP_HOST}/$1 [R=301,L]
Now subdomain1.domain.com won't redirect (or subdomain2/3), www.domain.com won't redirect, but anything else will.