In general, the cause of constipation in Tibetan medicine is due to low heat in the Digestive Fire, which translates most closely to metabolism in the allopathic system of medicine. In general, wrong diet and behavior causes the weakness in the digestive fire, and in your case it could also be related to the disturbance in the descending rlung (one of the five different types of rLung).

As well as the guidelines on diet and behavior in our question and answer library, I would suggest that you do some stomach massage and some stomach movement exercises. Perform very gentle massage around the stomach area, colon, lower abdominal, area and lower back. It does not matter how you massage, whether in clock or counter-clock wise manner, but the most important thing is to massage downward, pushing the energy down. Meditation to balance the rlung energy and breathing exercises are recommended. Always try to drink more warm or room temperature boiled water, including coffee or tea, instead of any cold liquid. It would be more beneficial if you sip some warm water after eating. Do not apply force when going to the bathroom, as it will cause more disturbance in the descending rLung, bleeding, and hemorrhoids and also could cause piles that are more serious to cure.