At what point do you seek immediate medical attention with what my doctor suggest are mitral valve prolapse symptoms that are persisting and worsening?

Never: Mvp doesn't cause symptoms and is never an emergency. Many symptoms are attributed to mvp but research has not confirmed any relationship. Mvp is a variant of normal. In rare instances, a tiny subset of people with mvp will rupture an attachment of the valve and develop sudden severe leakage which causes immediate heart failure. If you had this, you wouldn't be at your computer!