As the other posters have said, you really need to do past paper questions. Go through a full paper in exam conditions and see what topics you struggle with. Do this for both the calc & non-calc papers.
Once you've done that and found what you struggle with, do at least 2 questions a day on these topics. I'd also recommend trying to do at least 1 calculator and 1 non-calculator paper per week. Dip into other exam boards if you need it. Whilst I did my GCSEs, I completed every paper on my exam board (and repeated a couple), and it helped boost my grades immensely.
It's all well and good going over only the bits you struggle on, but you need to make sure you're well balanced and can still do the questions you think you're okay with. This is why I recommend a paper a week - it'll pick up on your weaknesses, tell you your improvements and also allows you to see your overall progression.
Also, as said before, i'd maybe reconsider your A-level choices if you can. If you feel like you can keep up with 4 subjects, i'd say keep your health and social care and pick up maths. If not, then i'd drop the H&S for mathematics. You'll be a much stronger candidate for an economics degree with A-level maths, as opposed to health and social. However, Health and social is an interesting subject in my opinion, so if you can, i'd do both.
Best of luck with your exams!