I haven't read all of the comments yet, but sidelaying nursing never worked well for me! I would sit up and alternate postions (football holl, cross-cradle, etc) and do breast compressions while you are nursing. Also, have you had your baby checked for tongue or lip tie?
tongue tie: http://www.kellymom.com/babyconcerns...tonguetie.html (text)
pictures of tongue tie: http://www.tonguetie.net/index.php?o...ask=view&id=12
I could not find a good link for lip tie, but google "lip tie pictures" and you will see some examples and links to stories.