An itch the way you describe it is most likely something
like jock itch, which is not a STD. I certainly would not go to the emergency room for it! You can get over the counter creams which will work. If you try that and they don't work, at that point I might get myself checked out. But I'd try that first, it's cheap and easy to do.
The only other possible risk would be HSV, which can be itchy. But since you have no sores, fever, etc, I doubt that's the case.