8 year old boy with social problems and poor attainment at school

I am becoming very concerned about my son. He has very few friends and is being bullied at school. I think this is caused in part by his attitude toward others - he does not seem to empathise with people and I believe he is a "tell tale" from what I have observed. He does not seem able to listen to anything people say to him - for example when speaking to him and immediately asking what I was talking about, he will make a guess which, no matter what subject, is wrong about 90% of the time. His attainment at school is very poor in all key subjects and his sister (5 years) is beginning to overtake him with reading. His teacher is regularly phoning me or my wife to report misbehaviour and has stated that she has not taught a child more difficult to motivate.
We have spoken to the special educational needs teacher at his school (about 1 year ago) but we are still waiting for an appointment at the child development centre. My concern is getting progressively worse because he is getting further behind at school and the bullying is starting to really bother him - he is not eating properly at home now because he is being called fat (which he categorically is not) and he is making up illness to avoid going to school. Does anyone have any suggestions as to what I can do to help him?
P.S. we have tried going to his GP!