can't load pg gem even after installation - ruby-on-rails

Question

Sorry if the question is basic and forms of this has been asked. My sysadmin is out of the country so I'm stuck trying to figure this out. And none of the similar question has the exact situation (believe me I looked and have been banging my head against the wall for some time).
See below for my ruby/gem, which are all 1.9.3. Then upon running it somehow shows 1.9.1, not sure why. Anyway I've tried installing pg, the missing gem. It looked like it installed but re-running gives the same error message.
Please ask me any other information you feel is relevant.
rails#alpite:~/solr_indexer$ which ruby
/usr/local/rvm/rubies/ruby-1.9.3-p551/bin/ruby
rails#alpite:~/solr_indexer$ which gem
/usr/local/rvm/rubies/ruby-1.9.3-p551/bin/gem
rails#alpite:~/solr_indexer$ ruby indexer.rb
/usr/local/rvm/rubies/ruby-1.9.3-p551/lib/ruby/site_ruby/1.9.1/rubygems/core_ext/kernel_require.rb:54:in `require': cannot load such file -- pg (LoadError)
from /usr/local/rvm/rubies/ruby-1.9.3-p551/lib/ruby/site_ruby/1.9.1/rubygems/core_ext/kernel_require.rb:54:in `require'
from /home/rails/solr_indexer/cfg.rb:2:in `'
from /usr/local/rvm/rubies/ruby-1.9.3-p551/lib/ruby/site_ruby/1.9.1/rubygems/core_ext/kernel_require.rb:54:in `require'
from /usr/local/rvm/rubies/ruby-1.9.3-p551/lib/ruby/site_ruby/1.9.1/rubygems/core_ext/kernel_require.rb:54:in `require'
from indexer.rb:1:in `'
rails#alpite:~/solr_indexer$ gem install pg
ERROR: While executing gem ... (Gem::FilePermissionError)
You don't have write permissions for the /usr/local/rvm/gems/ruby-1.9.3-p551 directory.
rails#alpite:~/solr_indexer$ sudo gem install pg
[sudo] password for rails:
Sorry, try again.
[sudo] password for rails:
Building native extensions. This could take a while...
Successfully installed pg-0.17.1
1 gem installed
Installing ri documentation for pg-0.17.1...
Installing RDoc documentation for pg-0.17.1...
rails#alpite:~/solr_indexer$ ruby indexer.rb
/usr/local/rvm/rubies/ruby-1.9.3-p551/lib/ruby/site_ruby/1.9.1/rubygems/core_ext/kernel_require.rb:54:in `require': cannot load such file -- pg (LoadError)
from /usr/local/rvm/rubies/ruby-1.9.3-p551/lib/ruby/site_ruby/1.9.1/rubygems/core_ext/kernel_require.rb:54:in `require'
from /home/rails/solr_indexer/cfg.rb:2:in `'
from /usr/local/rvm/rubies/ruby-1.9.3-p551/lib/ruby/site_ruby/1.9.1/rubygems/core_ext/kernel_require.rb:54:in `require'
from /usr/local/rvm/rubies/ruby-1.9.3-p551/lib/ruby/site_ruby/1.9.1/rubygems/core_ext/kernel_require.rb:54:in `require'
from indexer.rb:1:in `'

Answer 1

You're using a multi-user RVM installation to manage multiple Rubies. When using that, don't use sudo to install gems. The RVM installation page says:
Note: The Multi-User install instructions must be prefixed with the sudo command. However, once the install is complete, and the instructions to add users to the rvm group is followed, the use of either sudo or rvmsudo is no longer required. The sudo command is only to temporarily elevate privileges so the installer can complete its work. If you need to use sudo or rvmsudo after the install is complete, some part of the install directions were not properly followed. This usually is because people execute the install as root, rather than executing the installation instructions from a non-privileged user account.
I'd recommend reading that entire page as it has important information for using RVM with your environment.
The "Sudo" page is also good reading.