It is really difficult to diagnoses conditions over the internet as I would need to see it as well as do some tests. What I can do is give you some suggestions on what to do next.
Skin conditions can be difficult to diagnose as there are so many different things that can cause them. Most of them are not sexually transmitted. The best thing is to get a doctor to have a look at it while it is still dry and itchy. It will make it easier for the health professional to work out what it is.
