MVP will cause MV regurgitation (back flow of blood into upper chamber) and if serious it will lower the cardiac output with each heartbeat and the heart will beat faster and harder.
I have moderate to severe MVR and do not hve the symptoms you describe. The medications I take is an ACE inhibitor (dilates vessels for less workload for the heart) and Coreg. Coreg (beta blocker) keeps my heart rate within acceptable parameters and also reduces anxiety while exercising.
The problem could be your medication, thyroid problem, or/and other medical problems. You should report the exercise problems with your doctor as it is not normal to have the symptoms you are experiencing with exercise (ruling out extremely low physical condition).