Dealing with the PhD Blues

I like science. But...

- I can easily imagine other things that I would enjoy doing
- I am not sure what it is that we are trying to find (I guess I am spoiled by the Konvalinka's lab in this aspect) and this lack of purpose kills my motivation as well as it makes me wonder whether I am completely wasting my time
- I am not sure if one of my colleagues is not crazy
- without knowing it, I entered a particular area that, it seems to me, has been done to death

So...

either I carry on, find my own questions and purpose and finish my PhD in six to eight years OR I do something else. Hmmm.