Why is it so hard for me to poo when i want to?

Let's define problem: Doctors define constipation as stools less frequently than once every 3-4 days. Patients feel they are "constipated" when passing hard or small volume stool, or they feel full ; bloated. Had x-ray to show you're not blocked? Mabe your gut is sluggish or your anus/ rectum work incorrectly--these can be tested for (sitz marker study ; anal manometry, respectively). See a GI specialist.