Originally Posted by Doc V

Based on your position in picture 2 and the fact that you need to angle your saddle back to keep from sliding forward, your saddle is too far back. With your pedal in the 3 o'clock position, like in pic 2, your knee should be roughly over the pedal spindle. You can check this by dropping a plumb bob from right under the knee cap, the soft part right under the knee cap, down through the pedal. You will probably be a little behind that because the frame looks to be a bit small for you.

You can follow these fitting instructions to get a rough fit: How to Fit a Bicycle.