What Causes Leg And Knee Cap Aches After Childbirth?

I delivered my baby 2 months ago and my feet and legs have started to heart. About 2 weeks ago my feet started aching and then the other night my knee caps got really hot to the touch were red and achey. Now my legs and feet ache all the time. During pregnancy i started to develop preclampsia and had to be induced 3 weeks early. Went to the hospital already and they tested for blood clots in legs but none. any suggestions