Hi dear, Pain full defecation develop mostly from anorectal cases such as fissure in ano, hemorrhoid,abscess . An alternating constipation and diarrhoea are symptoms of Irritable bowel syndrome,but you have no any other symptoms such as abdominal pain, bloating, heart burn,dyspepsia etc,that help us to exclude the chance of IBS. Considering the symptoms that you had given here, I suspect a type of simple constipation may be caused from diet change, any medicines or psychological issues. Low fiber diet, less fluid intake, more caffeine,tea,alcohol all can induce constipation. Many medicine also cause bowel disturbances. So discuss with doctor if you had started any medicines recently. Lack of exercise can contribute a large towards constipation. For the management of simple constipation you can concentrate on fiber diet, bulk forming diet, reduce coffee, tea and alcohol. Take enough water. Perform regular exercise . These practices may help you to relive the condition. If you are experiencing the same, we have to consider more serious conditions and you have to consult with a surgeon as direct examinations are needed,he can help you after required investigations. With thanks. Take care