Welcome to the STD forum. I'll try to help.
On balance, yeast (or some other sort of non-STD inflammation) seems more likely than herpes, at least for your current symptoms. And certainly antibiotic therapy can lead to yeast overgrowth, which can happen quite quickly. However, herpes is always a consideration for penile sores. If that's what you have, a recurrnce of the possible herpes from 4 years ago seems is more likely than a new infection; 31 days is too long for first symptoms of a new infection.
If the penile lesions are still fresh (under 1-2 days in duration) and/or ulcerated and not yet healing, you could see a provider immediately for examination and possible culture or (preferably) PCR test for HSV. If that isn't practical, or if lesions are starting to heal, you should have an HSV blood test. If positive for either HSV-1 or HSV-2, it won't necessarily mean the lesions were herpetic, but would increase the likelihood; but if negative, it would exclude herpes for sure.
In the event this turns out to be herpes, HSV-1 seems more likely than HSV-2. Following symptomatic initial herpes, HSV-2 usually causes symptomatic recurrent outbreaks 3-6 times per year, whereas HSV-1 outbreaks are infrequent -- more compatible with a 4 year gap.
I hope this helps. If you proceed with HSV testing, please return with a follow-up comment to report the result.
Regards-- HHH, MD
Thank you Dr. Handsfield for a quick reply.
As an update: the redness has already started to go away/heal. It started this morning, and now, in the afternoon, it's has already started healing.
Does that mean anything?
A little quick for herpes, which normally would ulcerate and take a minimum of 7-10 days to heal. But that's still no guarantee. Speaking personally as much as professionally, if I had the symptoms you describe, I would get tested for HSV. I predict a negative result (at least for HSV-2), but why take the chance?