Enroll in a class not a part of a bachelor-degree curriculum. It could be sculpting, painting, photography, learning a musical instrument, screenwriting, a new language. Something to do with the arts with other creative, passionate people, that encourages participation and feedback with one another. It doesn't need to be something offered through a university either.
Join a weekly bicycling meet-up or a tennis class or something similarly outgoing and sporty. Physical group activity will also be a boost in endorphins, basically nature's anti-depressant. If you keep it up long enough your health will improve too.
Try perusing local alternative newsweeklies and such looking for interesting stuff going around town to attend. Street fairs or art gallery stroll nights are simple examples. Also outdoor concerts.
Good luck and don't get discouraged, or crawl back into a cave of introverted self-loathing. Be as open-minded as possible, otherwise you won't be open to real change.