you could self teach a level maths in two months full time
buy engineering mathematics by ka stroud, and try work edexcel up to fp3, so you can assess progress,
you can learn gcse maths in 2 weeks to a month of full time study,
use mymaths, and work through it, its very very easy, just get to grips with trignometry and other higher level stuff
cant believe i spent two years doing it lol, although i guess we did 11 gcse back then so fair enough
as maths is very easy, its pretty much memory, same with c3 and c4 i guess lol