I was reading in a magazine that if you are sore from moving a lot, and it isn't too bad, you should try to do that exercise again but not as long or as hard. Then when you are done do a cool down. You should stretch after you exercise because if you stretch before you exercise than your muscles might get cold and you have a more likely chance of injuring yourself. Try doing warm ups instead, like jogging in place or doing a few jumping jacks. When you are done you can walk if you were runneing or dancing.DON'T JUST SIT DOWN!!!
If you sit down right after an exercise the chemical in your body that was helping you use the stored fat in your body with cristalize and cause your mussles to be sore. When you coold down, you work this chemical out of your mussles so it doesn't hurt.(as much)
As for the singing. Try a few cough drops for when you get a sore throught, but don't take too much. Honey usually helps and if you happen to have the herb tyme(pronounced time) if you put that in some chicken noodle soup(not too much) and it could help your sore throught.(don't put the honey in the soup)
eat the honey on toast. If you happen to have unprossessed honey that is even better.
Also don't forget that you should warm up your vocal cords as well. You should also know that if you yawn a lot after a chior practice that means that you are breathing properly. You might also know by now that you should breath through your stomach (no matter how embarassing) so that you can hold a note out longer.
You should also try not to stress a note that you can't reach. If you are unable to reach a certain note than you should ask your teacher if there is a harmony note that you can sing or if you can just pretend to hit the note so that you don't look bad when you preform.