Your main concern is chronic constipation. Amylase level in serum is with in normal limit.  You should consult any gastroenterologist for evaluation. Colonoscopy and sigmoidoscopy are to be done to rule out any possibilities of any pathology in intestine. Chronic constipation is a serious symptom related with Irritable Bowel syndrome or Colon Cancer or Drug induced or Eating disorder or Change in exercise habits. Rx., Tab. Dulcolax 2tab once at bedtime s.o.s for severe constipation. Avoid diary products completely untill recovery. Make a habit of clearing your bowel in morning. Practise yoga twice daily. Take fibre rich diets mostly.