I dont think i could manage A level maths in 3-4 weeks, considering that you start with only having GCSE standard maths which is so very basic. I mean you barely know how to solve a quadratic to start with let alone dealing with trig, integration, vectors etc Its all relative to what you've studied before.
And yes you can self-study, why not? I do. Apart from M2, i dont have a maths teacher. The books are so comprehensive. If you get really stuck you could ask on TSR or one of the maths teachers in your school (you dont have to be their student!)