STD's are really not transmitted through just licking an area. I believe you have a very small possibility of that happening. And itching is not really a symptom of an STD.
I would try to apply some anti itching cream and see if that works.
Was the rim job with a guy or girl? Do you know this person are they clean? What was the person doing or you doing with them before the rim job? Where did the rim job occur (your apt, hotel, etc.)?