Except when there is overt, obvious trauma during sex (e.g., oral sex with playful biting that becomes too vigorous), almost no genital ulcers or sores are caused by injury. And certainly a sore due to injury doesn't first show up 2 months later. So although I don't like to challenge the diagnosis of a doc who actually has examined a patient, your doc was wrong.
By far the most common cause is herpes. I don't know what herpes test you had, but if it was a culture of the lesion, that probably isn't reliable; a positive culture always confirms the diagnosis, but a negative rarely excludes it. But if you had a proper HSV blood test at least 2 months after your exposure, then herpes probably isn't the cause.
However it started, it sounds like it has evolved or been superceded by something else--and your current symptoms don't sound much like herpes. Steroid creams (hydrocortisone etc) can trigger fungal infections; or you might have eczema, scabies, contact dermatitis, psoriasis, or something else. Also, steroids can screw up the diagnosis when you see a health care provider.
Stop the steroid and make an appointment with a dermatologist for at least 2 weeks afterward.
Good luck-- HHH, MD