Short fingers and finger strength don't affect your guitar playing. Instead, it's all about the way you position your hand. Look at your hand, from the bottom of your palm to the tip of your fingers. If that distance is greater than the width of the guitar neck, your hand is big enough to reach every string and play them clearly.

I have a feeling your thumb is wrapped around the guitar neck in a baseball bat-like grip. That will limit the reach of your fingers. Your thumb should be centered in the back of the neck, pointing upwards towards your face. It also should not point towards the tuning knobs...

Your palm should be jutting outwards away from your body.

You can see how this looks by watching this video of Jon Gomm: http://www.youtube.com/watch?v=nY7GnAq6Znw

When he's playing on the higher-pitched strings, his palm kind of sucks inwards towards his body, but when he's playing on the lower-pitched strings, it juts outward.