So when I play Hanon my wrist hurts when my right hand goes all the way to the left side of the piano. I try to keep good posture and lessen tension but it hurts. Only while playing and the pain goes away a bit after but yeah. Any ideas?
I agree with both posts above and will add that if your teacher cannot find the source of the pain, see a doctor or physical therapist. You may be doing something elsewhere in your life that is causing a problem at the piano due to the fact that you don't use your hands the same way throughout the day. One time, I had a student who was straining her wrists doing Yoga, but it showed up only at the piano. I injured my hand while gardening, but the injury was aggravated when I played piano, more than while doing anything else.
Dekkadeci is quite right, your weight on the buttocks is constantly shifting left to right as you play left/right on the keyboard. This enables you to keep the forearm aligned behind the playing finger without twisting at the wrist. Are you sitting too close to the keyboard? Check out The Taubman technique or The Golandsky Institute. There are heaps of videos on different topics on YouTube. I play Hanon every day and never get sore wrists. I would definitely discuss your problem with your teacher before the pain becomes chronic and you can't play at all!