I will try to explain the activity levels:
RED activity is where the brain is working the hardest. In CFS/ME this is not just physical activity. Its computer use, reading books (!!), watching any television that involves "thinking", such as a programme he really wants to watch, eating, personal care, craft activities. Basically, anything you would get DS to do to keep him awake. (which makes it so incredibly hard!)
AMBER activity is flicking through magazines that you dont have any interest in, watching programmes you dont really have any interest in,
GREEN activity is where DS would be awake, but totally relaxed, such as listening to quiet relaxing music.
I will explain what we did, so that you get an idea. Dr Crawley explained all this to us, but it was now 2 years ago, so I am a little rusty! DD3 was only allowed to have 2 hours a day "red" activity to start with, broken up into 20 minute "slots". When you think that getting up, dressed and downstairs would take at least one of these "slots", then each meal-time, another slot, she was really restricted. We learnt fairly early on that we needed a time table and we needed to stick to it with army-like precision. Her worse time was of an evening, but for the last hour before bedtime, no red acitvity is allowed, so we "saved" some time to finish just before her last hour IYSWIM.
Amber activity then made up more of the time. I cant remember how much now, but most of the day was made up with watching rubbish on TV. (she was 14 and watching winnie the pooh and mindless trash!- she started watching some snooker, which she started off thinking was really boring, but she soon became interested in the rules and who was going to win, so that was then moved up to a "red" activity, much to her annoyance. She was able to sort her bead-making stuff out on amber activity, but making her jewellery was "red". 
Green activity had to be done about 3 times a day for about 30 minutes, but without her falling asleep.
HARD HARD HARD!! Sorry, not very encouraging, but I have to say that we did this whole-heartedly and really did not cheat. It was really difficult and I sooooo wanted to give up. We were told to do this at the same time as getting her from 20+ hours sleep to 9, over a 2 week period. DH and I did out a routine, minute by minute for the 2 weeks and rigidly stuck with it. After 10 days I wanted to scream, rant and phone Dr Crawley up and tell her exactly what I thought of her crap schemes and how let down we felt. Day 14, DD slept 9 hours, she was a different girl and things really picked up from there.
Where you DS has already improved once already you may well find that he just needs less time to get back to where he was before this last dip.
On the subject of Dr Crawley, we are also well outside her area. But she travels around the country to see people. You should have had a specialist consultant referral done by now. (I believe it is within 6 months of diagnosis) It is in the NICE guidelines, that all GPs and hospital Drs have to conform to. There is information on the AYME website. It would be worth reading the NICE guidelines and going to see your GP armed with a plan that you wnat him to implement, using these. Have you been in contact with AYME? These people were my lifeline for years!! They are brilliant and know all the answers, or if they dont know the answer they find out and get back to you. They really were fantastic.
Sorry for long post, but I hope at least you get an idea what I meant. Please come back and ask questions, I hope I havent put you off!!!! 
Just never forget that he will not always be like this. Its awful now, but he has every chance to get back to a normal life and back to being your energetic, fun-loving DS.