Welcome to Connect, @wesm. Polycythemia Vera is a condition where your body is producing too many red blood cells. Your doctor has you taking Hydroxyurea to help keep the overproduction under control. Even so, there are some symptoms which may be associated with PV. Here are a few of them:
fatigue, itching, trouble breathing when you lie down
trouble concentrating, unintended weight loss,
pain in your abdomen, especially the left side where your spleen is located
feeling full easily, blurred or double vision
dizziness, weakness, heavy sweating, bleeding or bruising

There can also be some side effects from the medication itself. But what you’re describing with pain on the right side of your chest & back, along with your shortness of breath with the least bit of exercise, would have me making a trip to see my doctor or the ER, ASAP. Even though you’re being treated for this condition, those symptoms could be related to a heart condition or potential blood clots. Have you talked to your doctor about your concerns?