Why won't my sourdough form a shapeable dough that doesn't stick?
When I was young and poor I baked all the bread my family of 5 ate, for several years.  I baked yeast and sour dough breads with various flours. 
So some hints: 1. Use good bread flour! King Arthur's or Hecker's brand, if those are not available look for a high gluten wheat flour, if possible unbleached.
2. Get good at making yeast breads first.  Yeast is more efficient than lactoacid bacillus and will make bread rise better.  Once you have made a few batches of nice home style white, then try adding in some different flours.  I used to make oatmeal, rye and Anadamer bread.  All of which are variations on white.  None of them will rise as well due to the lack of gluten. Then add your sour dough to the yeast dough.  Yes, you can get sourdough to rise without yeast but it will take much longer and occasionally fail.  Adding the sour dough starter to a yeast dough will still get you the great sour flavor with the bonus of a better success rate.

3 There is no substitute for kneading.  You generally can't stir enough flour into a dough to make a firm bread, you have to knead in the last couple cups.  Your problem really sounds like not enough flour being kneaded in at the end. Your boule should be smooth and have a dusting of flour on the outside.  You can over knead, if the dough starts to tear rather than stretch just let it rest for half an hour.