Have you been bitten by chance by a spider? The venom causes blood clots and swelling. Any marks in your legs from a bite?
Hello~I am so sorry that you are having these issues. As the above poster said, it could be food or environmental allergies. It could also be a condition called "Candida" I would try an "elimination diet" this is where you start eating one food at a time and then gradually add another and another.
There are lots of sites on Candida, this is a form of yeast infection that starts in the gut but spreads to other areas, it can cause all kinds of symptoms. There is book called "The Yeast Connection" by Dr Crook" it is excellent, I think it can still be obtained from Amazon.
I hope that you find the help that you need. Blessings to you.
What kind of testing have you done besides the biopsy?
What did the biopsy find - nothing at all?
Have you tried tracking foods, activities, etc., that happen before this occurs? Really think of everything - since it's happening only on your legs and feet, think of everything that touches that area. Are you wearing a certain pair of pants? Doing a certain activity? Going to a certain place where you might be driving longer, sitting on a certain chair or couch?
Maybe it's a food you eat. We often think that food allergies have to give full-body responses, but my sister has some food allergies, and she only gets responses on the bottom of her feet.
If they aren't finding something internal, so to speak, look external, and get really creative when you think of possibilities.