Swelling back leg isolated below gastrocnemius to ankle. MRI, arteriovenous US normal. Tightness both sides of leg near ankle w/ dorsiflex. Tendonitis?

MRI of what? This is tendonitis the MRI should have picked it up. If it was a Baker's cyst the US should have picked it up. What else did these examinations show? You need to discuss with your physician the results of the tests and what was and what was not imaged.