Yeah, I had U/S about 5 times on mine, and it always was sore and tender and a bit more swollen than usual. Like goolarra says, it does get a bit beat up, when you think how much pressure they use. Poor old thyroid reacts to that.
Only if it REALLY suddenly swells up do you need to see someone at an ER. Otherwise it is quite normal to have some discomfort and minor swelling.
I don't think that's unusual. Even when your doctor just palpates your thyroid for a few seconds, it can cause some discomfort and swelling. It sounds like your thyroid was a little "beat up" by the U/S tech...maybe s/he needs to be a little more delicate???