My Knee Has Been Hurting For About 3 Weeks. It

My knee has been hurting for about 3 weeks. It started when I was on my knees doing some cleaning and it isn't any better. I have a hard time bending my knee all the way and if I sit for a long period of time, it's hard to walk on it for a few minutes. My name is Donna and I'm 51 years old.