Lonely and wanting a relationship

Hi,
I am a 29 year old woman, I've just finished a PhD and I'm tired of being alone.

For the past 5 years I have not had a single boy interested in me. I approach guys and always strike up conversations with guys but they never seem like they are interested, well there is no follow up. I make sure I smile, take care in my appearance. I was never worried about it up until now. After 5 years of no potential relationships occuring you have to start to wonder! The only potentials I've had tends to be married guys that want to get in my pants.

I have lots of male and female friends so I know I am likable. I try not to worry about it and just live an active and sociable life but I don't know that I can continue this continual rejection. Any thoughts would be great.