I had 344 of RAI and was sick as a dog and had swelling under both ears which was quite painful. Drink lots and lots and lots of water and it will go down, you can talk to the doc about compresses if it doesn't but flushing out should help a great deal. Watch your kidneys too, they get a workout and stones can develop, I ended up passing them after drinking straight lemon juice, I juiced about 5 the first day and also ate lots of parsley, both are good for cleansing. Teeth are very important too as onemoretime indicated above and your eyes, if you experience pain or swelling you should contact your opthamologist, mine recommended using artificial tears as the rai dries out everything soft tissue and the swelling went down on it's own but it did interfere with vision briefly but it was temporary. The worst is over, all the best.
The swelling could be a salivary gland. I had 200mCi for papillary in February '08 and have been having some problems with my salivary glands, most of it showing up in the glands below the ear lobe. Before that, I had no idea that there is a gland below the ear.
If you had spread to lymph nodes, the whole body scan you had before the RAI would have shown this. What did your scan show? Also, you should be having regular blood work to measure TSH and Tg; these numbers should go down if cancer cells are being killed off. You should call your endo about the swelling. Let them make the call.
And with such a big dose of RAI, you are likely to have some permanent damage to the salivary glands, usually dry mouth to some extent. See your dentist regularly, let them know about the RAI, and what meds you're taking as a replacement (Synthroid - and the generic- can cause dry mouth.) Take good care of your teeth, and drink lots of water to compensate for salivary damage.
Hang in there.