Good morning, @casevin7 It’s awful to feel so miserable. This sounds so disrupting to your normal, active life style. When you were initially diagnosed with secondary PV did you have a bone marrow biopsy? How were you diagnosed?

Do you recall if you’ve had a blood test for EPO? Erythropoietin is a hormone that tells the stem cells in the bone marrow to make more red blood cells. EPO is made by cells in the kidney and these cells release more EPO when blood oxygen is low.

One of the causes can be sleep apnea. Lung, heart and kidney disease can also be underlying culprits.
This article on erythrocytosis from the Cleveland Clinic might be useful information for you.
https://my.clevelandclinic.org/health/diseases/23468-erythrocytosis
When’s the last time you’ve been seen by your doctor? Have they checked for a swollen spleen by pushing in your upper left abdominal area? This is always one of the first things my oncologist does.
Are your other blood result numbers off such as your kidney function? Do you know if you have sleep apnea?