Hi, thanks for the to HCM.
Pain at one side around the anus means.
2. Fistula in ano.
There are three veins draining the blood from anal area towards upside.
They are situated in such a way that they resembles like at 3, 7, 11 o'clock as in a watch dial.
At which place there is pain you can feel and notice it.
This is the usual habit of a person that early in the morning when wake up, he or she try to pass stool whether there is desire of defecation or not.
If desire of defecation is there alright , stool will pass smoothly.
If desire is not than person will apply a pressure over abdomen to pass stool forcibly and this unnecessary pressure is the main reason of haemorrhoids.
When piles as a popular name is there person will feel mild itch at the site , mild pain , blood may be , as time passes condition worsen.
In fistula in anus at a particular site person feels pain excruciating and after some time there become hole ( fistula) and through this stool starts and foul smell comes.
You have constipation
so for this take fiber diet , if still no relief than consult a doctor and take some laxative which will soften the stool.