I'm having the same problem as you, OP. I literally can't revise effectively. I've tried reading books over and over, flashcards, having friends give me quick-fire questions, etc...but nothing's really worked. Maybe I'm just not motivated enough, since most times an exam comes, I've done fuck all revision and might only pass it based on rambling shit up that sounds a bit smart, but actually doesn't have much substance behind it.
Eh. I'm not sure there's anything that can be done about it. People can study for years and years. If you're bad at a subject, you're bad at a subject. If you don't like a subject, you don't like a subject. It's the unfair way of the world.