why is it painful to sit down?

When you sit on a firm surface you are actually placing most of your weight on to your pelvic floor muscles.  Pain with sitting is a classic symptom of your pelvic floor muscles being tender.  It is often associated with other pelvic pain disorders and is easily diagnosed by a simple examination by a trained provider.  It has been “popular” for some providers to quickly diagnose patients to have pudendal neuralgia when they have this symptom.  While pudendal neuralgia needs to be considered the vast majority of patients have pelvic floor tension myalgia.  Careful evaluation will clarify why sitting is uncomfortable for you.