Explain to us how you're revising. Are you just reading through the content and writing notes once? Do you revisit topics you've covered or do you just go from one topic to the next one?
You need to read through the material multiple times, close the book and then write down what you can remember, as well as asking and answering your own questions about the content. Look at the specification/syllabus for your subjects as well in addition to past exam papers. They'll give you a feel for the sorts of questions you'll be asked.