Suggest Remedy For Sore, Painful Knee Post Twisting The Knee

hello, I have hurt my knee, i'm not sure how but think I may have slightly twisted it walking down the stairs. It's been sore for about a week. It's fine to walk on but hurts to bend it and it's sore to touch, the soreness is on one side towards the front. I went to Pilates a couple of days ago and couldn't do many of the positions due to the pain when bending. I'm not sure whether I just need to rest it or if I should visit my doctor. Any ideas? Thanks