Help please: Compute the derivative function

Here's the problem:

$\displaystyle f(x) = \frac{2}

{{2x - 1}}$

Here's what I did so far...I have no idea if I'm even on the right track..

$\displaystyle f'(x) = \mathop {\lim }\limits_{h \to 0} \frac{{\frac{2}

{{2(x + h) - 1}} - \frac{2}

{{2x - 1}}}}

{h}$

$\displaystyle = \mathop {\lim }\limits_{h - > 0} \frac{{\frac{{4x - 2 - 4x - 4h + 2}}

{{2x - 1(2x + 2h - 1)}}}}

{h} = \mathop {\lim }\limits_{h - > 0} \frac{{\frac{{ - 4h}}

{{2x - 1(2x + 2h - 1)}}}}

{h}$