Check out unnecessarean.com
Also adventuresindiapering.blogspot.com (this woman has had 5 cesareans and has a lot of information on cesarean birth).
Some doctors will perform a 4th c-section. It would NOT be adviseable to try and have a vaginal birth after so many c-sections. It wuold be best for you to consult with several obgyns and find one who can assess your risks for a 4th surgery.