In the presence of psoriasis, you probably can't rely on the appearance to know whether or not the ulcer is herpes. You also can't tell the virus type, except that genital HSV1 rarely has such frequent outbreaks as you have but HSV2 sometimes does. And since your ulcer has come and gone anyway, it's improvement after starting Valtrex also doesn't necessarily mean you have herpes. It is true that recurrent cold sores means you probably have HSV1, but that also means HSV1 is not the most likely cause of your genital ulcer.
All things considered, my guess is you don't have genital herpes at all. But if it comes back again, see your dermatologist for another swab test (PCR, i.e. DNA test) when the lesion is only 1-2 days old. That's the best timing for a reliable result.
I had a recurring sore to clarify...for 3years. Prior to being diagnosed with herpes, l treated my genital psor.and the sore with triamcinolone, . It would go away but return within a month. The sore that l currently have was not treated with anything and has remained a sore for a month until taking valtrex. I had a swab for herprs but came back negative. Dna and bacterial tests also neg. I have had oral cold sores so l would probably test positive for 1. I will get a blood test next month from my gp. Is there any difference in the way the 2 different types look when they first appear? Thank you for your time.
"I have had a sore for 3 years" suggests the sore was there the whole time, but "it always comes back in the same place" seems to mean it comes and goes. Repeated sores sounds like herpes but not a continuous one for 3 years.
And what does "I have the cold sore virus" mean? Have you had a blood test? You say the swab test didn't show the virus? Find out what tests you have had and whether it shows HSV type 1, which is the usual cause of cold sores but sometimes causes genital herpes, or HSV2, the usual cause of genital herpes.
The usual outbreak of herpes of any type usually starts with a red bump that becomes a blister then an open sore or scab and then heals over 1-2 weeks. But almost any genital sore can be herpes, and other skin problems like psoriasis could make it different than normal.