How far along are you? I don't think it's contractions. If you are far along, I'd say you have a lot of weight on your legs. Try to stay off your feet. Prop then up while u lay down. Like 4 pillows high. I'm sorry u r feeling bad. It will be over soon.
I've never had knee pains with contractions but I get serious knee and hip pains in pregnancy because of the extra weight!