Either way, things got worse when you took antibiotics because this sets up a situation where
yeast infections are likely to occur, as it did to you (perhaps twice). Finally, all of these factors are exacerbated potentially by your psoriasis. Indeed psoriasis can effect the genitals and even if it does not, it suggest you tend to have sensitive skin.
Bottom line, what you describe does not sound like herpes. You have other, very reasonable explanations.