I am constipated rather frequently even if i eat plenty of fiber and always drink water. i take senna when i need to, but what could be the cause?

A sluggish colon: A common problem is a very sluggish (moving material through) and efficient (removing water from the stool) colon. A problem when you have bloating and discomfort as a result - but not a problem with absorption of "toxins". You need to help your colon to be more active. Senna is bad - you develop a tolerance and become addicted to it. Stool softeners, mom, glycolax are ok, even daily.