What causes rectal bleeding? It only occurs after bm.

Many. Depends on age, other medical issues, etc. List includes, hemorrhoids, fissures, colitis, polyps, avm (superficial blood vessels), cancers and more. Get it checked please.
Rectal bleeding. Rectal bleeding can happen due to hemorrhoids, polyps in the colon, inflamation in the colon, colon and rectal cancer.You need to see a gastroenterologist and have colonoscopy done to find out where the blood is coming from.