Re-reading a chapter is one of the most comforting things you can do while studying and one of the least useful. Your eyes move, the words are familiar, and nothing new sticks.
The alternative is to close the book and write, from memory, everything you think the chapter said. Mark what you missed in a second colour when you open it again.
For maths and physics, replace 'write' with 'do': pick one hard problem and solve it without notes. If you can't, that is the diagnostic you needed.
Do this after every session, not once a week. The pain of realising you already forgot Monday's material is the mechanism.