Does this comma make any difference in this sentence?
He decided to see the doctor about the problem(,) which had been bothering him.
I wish I had better English, but I work hard to improve it. I'm studying for IGCSE, so I'm only interested in BrE.
I don't think it ends up making all that much difference. The same problem is indicated either way; we're just not clear whether the second clause was planned well in advance, or strung on the previous one as a near-afterthought. Consider, for instance, on the other hand:
His brother put on the new Led Zeppelin record, which he found irritating.
His brother put on the new Led Zeppelin record which he found irritating.
In the first case, the irritable fellow may love Led Zeppelin, but could have been bothered by the fact his brother put one on -- while he was trying to concentrate on a novel, for instance.
In the second case, it is much more likely that the content of the recording was the problem, not the brother or his timing.
Does that make any sense?