This is certainly possible to do, but will depend on your hosting setup.
If you are able to create a wildcard DNS entry, you can map all subdomains of agrimgupta.com to the same IP address. If your web host is giving you a dedicated IP address and using an IP-based virtual host, these domains will all point to your web application. You could then use mod_rewrite or a custom index.php file to route the requests to different resources based on the subdomain.
Note that you will run into some hurdles here trying to re-map files to the proper directories.
This sample mod_rewrite code will do a simple redirect when you access blog.agrimgpta.com and point the user to the files under /oranges. The user won't actually be "browsing" under blog.agrimgupta.com however - that will take some more effort to accomplish. (At that point, you may just consider switching to a web host that will support multiple domains/subdomains.)
<IfModule mod_rewrite.c>
RewriteCond %{HTTP_HOST} blog.agrimgupta.com
RewriteRule /$ http://www.agrimgupta.com/oranges/ [R=301,L]
</IfModule>