This doesn't sound much like herpes, but I can't say that it isn't. In general, herpes is the most common cause of genital sores that become scabs. You'll need to see a health care provider for diagnosis, especially if such a lesion reappears or you get other symptoms, particularly if they are blister-like. If you have herpes, you didn't necessarily get it during the sexual encounter you describe.
As to other possible causes, I really cannot speculate. Any of the hundreds of things that cause rashes anywhere on the body sometimes can occur on the penis. The apparent reponse to cortisone cream doesn't help much; herpes outbreaks heal in a few days anyway. But it doesn't sound like anything dangerous.
Good luck-- HHH, MD
would a single lesion that has remained unchanged for 2-3 weeks but causes considerable pain be characteristic of herpes?
No, but conceivably it started at herpes then got perpetuated as a traumatic lesion due to trauma. I don't think this is herpes, just cannot be certain.