Why would it hurt to poop? but there's no visible hemorrhoids

Constipation: If your bm is hard or large, it can cause pain. You may also have internal hemorrhoids that you cannot see. You should be seen by your doctor if it continues, as it could also be inflammatory bowel disease.

Pain is not internal: Internal hemorrhoids usually present as painless bleeding. Pain in the anus with a bowel movement is usually due to an anal fissure, with sharp tearing pain during a bm , and variable spasm pain after the bm. If you are having painful bm's, it is best to be examined by a colorectal surgeon and learn of options available to treat this.

Anal fissure: An anal fissure is a good bet. Pain and possibly bleeding that is associated with a bm can be an anal fissure. It typically resolves, only to return at the next bm.