Well, Kam, it doesn't necessarily mean that you're no good, either. Sometimes, even very nice people lack some of the social skills that make it easy to start and sustain a relationship. It's had to tell, from the outside, what may hav gone wrong within these recent relatonships of yours. Have you ever been able to ask the guy ? Not as a big, emotional scene, but simply on parting, to say --- we had fun, it was pleasant, but the steam seemed to go out of things after a few dates --- can you do me the favour of giving it a little thought, and telling me what your view is of why things didn't work out ?
Of course, a psychologicst can provide counselling that can include considering one's social skills, and examining in more detail what happened in the relationsips that failed, to see what can be leaned from them.
But don't let your self-estem and self-confidence drop. You ARE a nice and fun person. If you enter into any relationship expecting failure, failure is almost guaranteed.