I Am Having Pain Behind My Right Knee With Shortness

I am having pain behind my right knee with shortness of breath, pain in both lower extremities that is made better with warm baths, and restless feeling legs especially at night that has started to cause me trouble sleeping (almost like an impending doom feeling). I don't have never smoked in my life, I am fairly active and don't sit for long periods, I'm not on birth control. I did have a baby 16 months ago with a c-section and tubal ligation. Can you help with what I may have going on?