Humanoctopus, I can identify with the feelings you are having at the moment. Our Paed did exactly the same thing re. diagnosis and sent us off. I cried for about 4 days, didn't sleep, didn't eat, didn't know what to do. School were equally unreceptive.
I would suggest:
Take time out of school for the rest of the week - just as you would do in "normal" circumstances if you had a child who wasn't able to move and had no energy.
Read the old threads. They took me a long time to read, but I learned so much ( it's what I did through my sleepless nights!)
Contact AYME - there is so much helpful info.
Also the Royal National Hospital for rheumatic diseases CFS pages. That's where Dr Crawley is, and their website has a lot of really useful info inlcuding activity diaries etc. Pacing is well explained on the AYME site - and will help you understand what is meant by baseline. It took me ages to work that out.
Start the melatonin - what dosage have you been given? My dd is yr 4 ( almost 9. v. small) and she takes 3mg melatonin and 4mg circadin (slow release melatonin) and that just about keeps her asleep for enough hours.
Eating and drinking - we've had the help of a dietitian as my dd lost a lot of weight initially. Little and often is the key. Just try to find what he thinks he can manage and even if it's only a few mouthfuls at a time, persevere. ~We also used paediatric supplement drinks which were given on prescription.
We waited over a year to see Dr Crawley and I wish we'd gone to her as soon as we could. Although we had a paediatrician and nurse specialist my GP was v. happy to refer us to Dr Crawley. GOSH don't see pre-teenage I think so Dr Crawley was the only person we could find who saw primary age. It's not a problem if you're out of area for her, and as someone else has said if your ds is too sick to travel she will come to you for assessment.
Don't underestimate the exhausting nature of ordinary activity for your ds. For my dd, getting dressed, eating, car journeys, being around other people, noise , light etc were all v. difficult, and I took quite a while to realise / accept that.
I've got to go, but hope these things help. I'm sorry you too are going through this. I think it can be v. hard with primary age, as it's so uncommon. we've battled with schools so I can tell you more about that later. I'd be happy to talk but I don't know how we go about giving numbers without posting them. What area of the country are you in?