You should be doing some simple prep which is going to make your life a lot easier. If you can, start compiling cheat sheets for the subjects you are doing, so after each class write down the key points that you will need to remember for the exams.
You could do the index cards and mind maps the same way.
For my exams, I did this as I went along last year, and it worked out well for me, as I passed with good grades. The brain will build better recall pathways if you remember over time, so just tick over for now, doing something every day. Then depending on the subject start getting your head down wit a revision plan about 6 months before the actual exam date. By then you should already have a good memory of the subject and be tweaking things that need your specific information and not the whole subject matter.