I seriously doubt this has anything to do with herpes. You received oral sex with a condom – good job with that – and had extremely minimal contact between your penis and her genitals, if any. With the sun and heat, this may well have been a mild fungal infection in the groin. If you are still concerned, you could try treating it with an over the counter antifungal medicine or see a provider in person for a better evaluation. but I seriously doubt herpes as a cause of the rash.