I completely agree with 'Dougieowner'. I've just taken my English A2 exam, and I wouldn't say it was easy or hard, because the marking is always so subjective. I've always known that I'm pretty good at English Lit, but I can never know for sure how an essay/exam has gone until I get the mark back. (I ended up getting a high A at AS level last year, but was very shocked to find that out - two of my friends got Bs, and they've always been top of the class students).
All it comes down to is whether you are prepared to put a lot of effort into it - of course, if you know the texts well and can write a good essay on poetry, then you are bound to get a decent grade. If you have a naturally 'flowy' essay style (which you probably do as you're keen on history and sociology), then you should have no trouble!
Finally, psychology is definitely not a well-regarded A level subject by unis (generally). English literature is one of the fundamental subjects; English, Maths, Science. An A in English Lit will definitely be more impressive than an A in psychology. Plus, even if you wanted to do something like psychology/sociology at uni you wouldn't even need to have studied those A levels, as not all schools offer them. My school doesn't offer either!