How To Treat Severe Knee Pains In Both Legs?

i am having severe knee pain in both knees. I am over weight and have put on over 70 pounds in the last year (227 5'7) I have never been over weight before in my entire life. I think that between an increase in psychiatric meds, cortizone injections, and oral steroids, the weight was inevitable; however the knee pain was sudden. He hurts to sit down and to stand up but not to walk or stand or sit. . . .just the motions of the preceding. I am of my medication for narcolepsy (nuvigil) is causing the pain or if fact it is my weight. I am slowing loosing weight. Please advise.