It's hard to say whats going on with your legs, but I wanted to throw out there that maybe you could ask for a sleep study. I know that sleep studies can be done for things other than sleep apnea.
You may have a sleep disorder and they might be able to DX and get you on a medication to help with the condition.
I've had lupus for over 26 years now and I'm fatigued and exhausted all the time. I do have central and obstructive sleep apnea. I'm always cold, but I'm also really anemic, to the point where I need blood monthly now.
I hope you can get this figured out soon. Please let us know if you find an answer for this problem. By the way welcome to the forum.
DX- RA, Lupus, Fibro, LGL Leukemia, Obstructive & Central Sleep Apnea, Pulmonary Hypertension, Bells Palsy, Gastroparsis, Blood Clots, Glaucoma, Chronic Pericarditis & Pleurisy, Severe Anemia. Way to many medications to list.