question about knees

Hi all: two years out and I find my legs get more tired more quickly and my knees have begun to hurt and every so often my right knee especially will start to buckle-not all the way but enough that it hurts my knees. I find my knees aching and this is a new symptom for me. Have other people developed problems with their knees and does this seem a result of leg weakness in general? At the same time I developed pain in both legs-again especially in the right that feels as if I pulled a muscle in the thigh-it is so bad I have to lift my leg when I get into a car or onto bed. It has lasted for weeks now and I did nothing out of the ordinary to cause it. The increased tiredness in my legs is disturbing as I hoped that would get better not worse. I find myself lying down much more frequently than in the past. Best to all, Jeff