So you consulted a professional, and a specialist at that, and now doubt his/her diagnosis. This is normal. I too am a clinical psychologist and I disagree with the previous psychologist - you don't have to be a mental helath professional to prescribe antidepressants, mood stabilisers or antipsychotic medication. Many medications have multiple uses; some antidepressants are used to treat pain, another antidepressant is used to stop bed wetting, anticonvulsant medications also act as mood stabilizers for bipolar mood disorders, antipsychotic medications can help to manage aggression, while others are used to sedate patients.
I do however agree with the psychologist and suggest that you shoud only medicate an acurate diagnosis. I am not sure what all you have had done for your child. Have you ruled out hormonal problems, liver and kidney problems, neurological problems, developmental problems etc? Could it be a chromosomal? It may be due to severe ear ache or some other "innocent" cause.
You mentioned febral convultions. These can affect thought processes as well as behaviour. The child can act erratically and often dangerously. Another golden rule for psychology and psychiatry is to never make a diagnosis until medical conditions have been ruled out, and further more, that the condition is not due to a chemical, drug or other substance. I would focus on these areas first. A physician may not be a bad person to consult next.
Ruling out all of these possible causes/problems can be costly. You can (will) be shunted from pillar to post and can be exposed to psychologists, psychiatrists, neuorologists, paediatricians, physicians. physiotherapists, occupational therapsits and more, often with conflicting advice and diagnoses. And apart from the expenses it can take a huge emotional toll on you and the rest of your family.
My advice, for what it's worth:
Surround yourself with a good network of support
Get educated - read, ask questions, and consult widely
Not all medication is indicated, not every person reacts the same to medications (often have to rely on trial and error)
Not all medication is evil. There comes a time to medicate.
You may find that you are faced with more difficult choices and tough news - you may hear a diagnosis that is "harder" or "more serious" than others. Sometimes the truth is difficult to cope with. In which case, refer to my first point of advice.
Most importantly, good luck.