Just beg to be allowed to get into A2 for the three subjects that you want to continue with (btw do you not have 4 AS levels?). That is all that you can do; make it clear that you didn't work quite hard enough all year and didn't revise well or effectively and had bad days in all exams. This shows that you clearly didn't reach your potential and may convince your teachers to allow you to enter A2.
Then you're up against it; you need to resit virtually every unit in january and then take the A2 units in june. I would apply this year for medicine and ask your sixth form to not cash in your grades so you can apply hopefully with pending for every unit and AAA predictions. Anyway, you'll need to work very hard, start now with revising AS and just go all out for it as you need to get up to AAA standard for medicine.
I doubt that getting a remark will help much; how likely is it that all the papers you sat were marked wrong? Not likely i reckon. Anyway, do you have module scores and did you get A's in those coursework modules cause if not (a lot of peoples drop grades) then you need to get them remarked to get A's.