I want to run the bathroom fan and light separately. I want to run and attach a 14/2 wire from the fan to where the light switch is. The question is, where do I get power for this new switch (for the fan). Can I somehow use the black and white wire currently at the light switch to somehow power my fan?

Is this a new fan? Fan only, or light/fan combo?
What is there now existing?

Thanks for the quick reply. This is a separate light and fan. The main power source is going to the light junction box on the ceiling. There are currently three devices which feed off this source: a motion sensor for the outside, another light for hallway and light within the bathroom. The bathroom fan is attached directly to this ceiling light and as a result both the fan and light come on at the same time. Can I somehow get power from the light switch on the wall (which currently only a has black and white wire) to power my fan separately? I want to bypass that mess at light junction box on that ceiling if I can.