I am a healthy 45 year old male. I regularly suffer from constipation which can last 2 or 3 days. I do not take any medication for it and it seems to resolve itself. I try to eat healthy and have fibre in my diet and drink plenty water. Advice please?

Constipation. Fluid intake in critical drink about 2-3 liters /day and also vegetables like greens, sweet potatoes, strawberries, avocados . Grains like bran while helpful in moderation if eaten too much can be constipating as well.
Fiber and water. Fiber foods: You may take a fiber laxative like Metamucil and drink enough water daily so that your urine is colorless. For the long term you may try to increase your intake of fiber foods. Consult this site for fiber foods.
http://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/high-fiber-foods/art-20050948.