WHY AM I ALWAYS F****** CONSTIPATED ?

I have always had problems with constipation when travel ling but these past few months I have been extremely constipated no matter what. At one point in time I was taking iron pills which is supposed to make you constipated (that was in the summer) but I was not nearly as constipated as I am now. I only go once or twice a week maximum. I eat an extremely high fiber diet and take fiber pills. I run every day and lead an active lifestyle. I don't really notice I haven't gone until the fourth day when my stomach is extremely bloated and I can feel everything inside. I just want to know why I get this constipated because it definitely is not due to a lack of fiber or exercises. I drink enough water also.