Same here. We did have a short break betweek sitting the early autumn state selective exams, then went to the seaside for the half-term, on the understanding that we come back and plug back into the same rigorous routine until Indies are done mid-January. To say it was hard to get him back into "a paper a day" routine is....er.... an understatement
However he clearly understands that that's his only option to get into a decent school (where we live primaries are good but secondaries are abysmal, and the only decent comprehensive is a commute away and massively oversubscribed). So we did visit the Indies he wanted a couple of times, and he is very excited and has the goal clearly in his mind. Having said that he's still moaning that he has to do lots of math which he hates (he's more on the literacy/arts side naturally) so it's tough. I'm also exhausted as have to keep a track of his studies, liaise with tutors and generally help him stay upbeat and motivated... it's just 8 weeks until he sits the last Indies exam and then I feel we'll just completely collapse
But at least we'll both know we made every effort, and the rest is God's will.
Hold on there, it's tough but your DS is not alone (neither are you), it will soon be over!