Title of this war novel?

I didnt get a chance to finish this book and really wanted to get to it... I remember it being set during the Vietnam war and this really young kid going over there to fight (14-16 I don't really remember). I also remember the kid's friend putting some sort of ointment in his lips given by a vc villager and his face was messed up and the kid got sick at one point and had diarrhea in which they called "the sh*ts". Really appreciate if anyone can tell my the title of this book.