fecus smearing in school

I just read a post about a boy 7 years old who smeared fecus.  I too have a son who had anxiety problems in school & was put on prozac in the second grade.  Within one month he was manic and smearing fecus in the school bathrooms.  He was diagnosed with bipolar and later Dyslexia, and LD in math.  I have wondered why he did this behavior was it due to the prozac or was he that unhappy in school.  At the time his anxities with learning where in the severe range.  He was literally pulling out his hair and going bald.  What do you think?  I have read that can be a sign of sexual abuse.  We have never seen any signs of sexual abuse.  My son is now 12 and still suffers greatly in school with the LD.