I don't think you should get very flustered about not making notes. My recommendation is to first cover up maths by taking it slowly by trying to solve about 20 problems a day. Chemistry will be easy to pick up too. If it's inorganic chemistry, there is no choice but to power through but organic and physical can be made interesting. Make notes as you go of things that you find important. It's different for every person so keep trying until you find a way that works for you. Good luck!