Your doctor will try to exclude worrisome causes, like cancer (especially if you are older than 50 years). He may do a colonoscopy, a CT colonography, a barium enema or some form of screening.,
He will also go through your history to see if you have any medical conditions predisposing you to Constipation.
After excluding any mechanical cause of obstruction, and if your doctor tells you that you have functional constipation, he may evaluate you further to see if you have a slow-transit colon ('sleepy' colon), or pelvic floor dysfunction (discoordination of your pelvic floor and 'pooping' muscles) by ordering transit marker studies or defecography studies.
Slow Transit Colon
Sometimes also known as a 'sleepy colon' or a 'lazy colon' or 'inactive colon', it essentially means that the colon moves slowly and hence propels the stool in the colon slowly. The colon is a muscular tube that connects the small intestines to the anus. It propels the stool that comes out of the small intestines towards the rectum and anus.
Pelvic Floor Dyssynergia
Also known as puborectalis paradoxis, non-relaxing puborectalis, Pelvic Floor Dysfunction, it is a discoordination of the 'pooping' muscles. In essence, 'pooping' involves the coordination of several muscles. Your abdominal muscles need to contract and squeeze the stool out, and at the same time, your anal sphincter muscles need to relax and open up to let the stool out, and your puborectalis needs to relax and let the kinked rectum straighten up so that the stool can pass out easily. In Pelvic Floor Dyssynergia, the puborectalis contracts even more and kinks the rectum further so the stool has more difficulty passing through.