A southwestern Illinois teenager has been charged with aggravated battery and criminal sexual assault for allegedly attacking a pregnant teenager at his high school.  The Belleville News-Democrat reported Tuesday that Saint Clair County prosecutors charged 17-year old David Fields of Shiloh as an adult.  Authorities allege the attack happened Friday afternoon at Belleville East High School, and Fields was arrested at a Shiloh home hours after the attack was reported.  Police say the pregnant teen knew Fields.