It can be due to fissure or piles.

You have developed a anal fissure which is quite common in people with the work of prolonged sitting resulting into constipation and whenever you pass a hard stool it is scratches our inner lining of Anal mucosa resulting in formation of anal fissure Kindly consult with your detailed history and specific comment on is there any blood discharge also per rectally while passing stool. Can we managed with lifestyle modification few dietary changes and supplemented with medications