You could have any of a variety of forms of wrist overuse injury. I've been there from music, and I used to work in the sports world where this is endemic. The bottom line is it doesn't matter what specific form you have, carpal tunnel, tendonitis, bursitis, etc, they are all different forms of inflammation from overuse. Your connective tissue grows slower than muscle, and a sudden increase in workload (say from nothing to consistently doing 1.5h a day) can easily do this. It's extremely common in music school where everyone is suddenly practising twice as much as they used to. I had chronic wrist tendonitis from the combination of saxophone and juggling. You might have some other problem, but this is the most likely situation and the fact that it is hurting when you are not playing means you need to take it seriously right away. If you do a lot of computer typing, the combination can be much worse than either in isolation.
You need to stop whatever you are doing NOW. Go to your doctor and get recommended to a good sports medicine person and physio therapist, they can show help with immediate symptoms and show you how to stretch properly, change your practise routines, and strengthen antagonist and stabilizer muscles to help prevent this. But the bottom line is you NEED to rest until there is no pain and then another week or two before resuming practising. Reschedule your exam, missing the exam is nothing compared to the hassle of chronic tendonitis for years. You will find other musicians who tell you how to deal with it and keep practising. They are WRONG. The world is full of musicians who have wrecked their careers/hobbies with chronic lifelong overuse injury by refusing to take the time off to heal now.
When mine got bad, I had to basically just do other stuff for a year, but now I'm totally fine. A year seemed like forever when I was 20, but now that I'm 40 and can still practise 3 hours a day without issue, I'm so glad I learned how to take care of myself. I cringe when I see young people icing and taping and then continuing to wreck themselves. That kind of thing is ok for pro athletes who have a million dollars riding on the season, but they are trashing their bodies and have off seasons of extremely expensive medical treatments to make up for it.
Good luck! Good physiotherapists are worth their weight in gold!