2nd mistake: ineffective treatment at the late stages.
Doctors often prescribe the "default list" of medications against anal fissures, but 90% of them are only meant to relieve the initial symptoms. Truly effective medications are rarely sold in pharmacies, since if everyone were to be cured, where would profits come from?
If you have blood in your feces, itchiness or pain in your rectum, or a burning sensation when defecating, it means that you only have a few months until you develop purulent paraproctitis; regular creams or suppositories will not help you anymore.