My Son Cannot Pass A Bowel Movement. I Have Given

my son cannot pass a bowel movement. i have given him medicine to use it. he is passing some liquid stool but says that he feels like there is something stabbing him in his bottom. his stomach hurts and he is having sharp pains and says he can't move when they happen. he is not eating. he looks bad and is not moving well. can constipation cause this or is constipation a symptom of his problem.