I'm not sure you're even allowed to post on MN if your DC doesn't achieves 6s and above! 
Seriously, he has English, that's great! 
There are plenty of parents of lazy boys on MN...luckily fir them they seem to be quite bright and pull off decent grades. If your DS isn't academic it's not his fault, so he shouldn't be given a harder tone than a bright lad who did no work.
As Steven Fry said on TV this morning, GCSE results matter today, but they won't matter in the end.
I think you just need to get practical, sort out what he is definitely going to do next year and order a pizza and ice cream.
Is he better than his friends at anything? Can you find a photo on your phone if him doing something his good at, pretend you've accidentally found it, show it to him and say "I don't know anyone else who is as kind to their nan as you/can score a goal like that, just show him that you really value him for who he is.
I know more than one person who's got through life on charm and a bit of focus in the right direction!