get together with group of "true friends" and ask them to truthfully tell you why THEY think you are single. Sometimes what we don't see in ourselves is obvious to others. Maybe they will give you some food for thought and some traits to work on. Also, I agree that you are probably trying to hard. Someone gave me advice one time that instead of "looking for Mr. Right" I should focus on "becoming Miss Perfect". I think sometimes we are so intent on finding the one that we forget to break bad habits, develop talents and hobbies, learn the art of conversation, read and become intelligent and interesting etc.

Finally, forget bars, the internet and dating agencies. I mean really? No one in their right mind would look for a QUALITY spouse in those places. If I met a guy and he told me he had used those avenues I would probably run as fast as I could.
Places to find quality people:

CHURCH
through friends
clubs (learn a new hobby)
work

Lastly, learn to be happy with your life whatever circumstances you find yourself in. No one has a perfect life. People are drawn to positive people and don't want to be around depressing ones.

Good luck!