I'm not applying for law but I'm in year 13 studying English Literature, English Language and History
IT. IS. A. LOT. OF. WORK.
However, that is hopefully not a shock as all a-level subjects are hard but be warned that all three have coursework and so depending on your school's system, you'll end up doing a lot of it over the summer/year 13 - the main reason why I decided not to do the EPQ in the end as that is in itself a whole subject essentially
As has been said, there are no required subjects for law
If you want to do psychology or economics, go for it! If you like all three subjects stick with them!
{Unfortunately, I have learned the hard way that if you are only half-interested in English Literature it will be an incredibly hard subject}