If you don't find GCSE easy and you are not enjoying it then probably don't take it. Alevel maths isn't easy and you have to work hard so enjoying the subject helps. however it depends what you want to do in the future.
i wuokd reccomend taking it for as if your good at it. Also depends how could you are in your other subjects atm and what you wont to do in the future! Maths at as is hard but a lot of it is exam techinque ,learning how to answer certain questions.
it really depends on what you want to do in life, look up what sort of course you want to take in uni and can do so throught ucas (http://www.ucas.co.uk), then you go to course requirements and see if it needs maths, if it is unclear, phone the university of the course to enquire, this is probably the best way, also you are getting good grades so far, so although it is not one of your best, it is a useful A level to have.