Symptoms depend on the type of HSP inherited. The main feature of the disease is progressive spasticity in the lower limbs due to pyramidal tract dysfunction. This also results in brisk reflexes, extensor plantar reflexes, muscle weakness, and variable bladder disturbances. Furthermore, among the core symptoms of HSP are also included abnormal gait and difficulty in walking, decreased vibratory sense at the ankles, and paresthesia. Individuals with HSP can experience extreme fatigue associated with central nervous system and neuromuscular disorders, which can be disabling. Initial symptoms are typically difficulty with balance, stubbing the toe or stumbling. Symptoms of HSP may begin at any age, from infancy to older than 60 years. If symptoms begin during the teenage years or later, then spastic gait disturbance usually progresses over many years. Canes, walkers, and wheelchairs may eventually be required, although some people never require assistance devices. Disability has been described as progressing more rapidly in adult onset forms.
HSP don't cause pain very much, I think you should see a neurologist. I think diarrhea and constipation have nothing to do with this pain.