There aren't many high paying jobs that you can get with just your GCSE's but that doesn't automatically mean you won't be a success (look at Alan Sugar). There are always more practical courses that you could take, you may be better suited to that sort of thing, academics are not for everybody. Have a browse on the internet and see what you can find, you could also see what internships are available. I hope this helps.
there are uni courses based around creative writing, My friend has just got onto a course for illustration and creative writing, which sounds really interesting, could be of intrest, illustrations really quite similar to graphic design
if i was to give you any advice it would be dont necessarily worry about the future just focus on what things you like doing and do a course on something your interested in and will therefore do well in, how about doing more vocational qualifications like BTECs rather than Alevels if your college offers them? you'll find that you may be able to do a course in creative writing, or IT and graphics, that may be a bit more suited to what you want to do, maybe more based on getting a job rather than just getting grades and getting into uni (if your not sure about uni yet?)
to be honest with you i just did A levels,but im currently on an art foundation course and a lot of my friends and people on the course did BTEC's and they seemed a lot better.
again if i could give you any advice it would be to remember that GCSE's, A levels are just something you have to do in order to get to the next stage of your life, for the most part, but in years to come they wont matter at all, so just make sure your doing something you want to do to make it worth while
not sure if i've really helped, but i think i know how your feeling, and even though i struggled with it i did go down the more 'conventional route' of a levels, uni, etc but again keep in mind there are other ways, like internships and apprenticeships, getting a job and working your way up, so dont be disheartened, there are plenty of options for you