What shots did LO get? My DS got the MMR/Varivax/flu vaccine and typically has a reaction to the previous combination, but didn't have anything- not even sleeping more or fussiness- this time.
I would also try ibuprofen- I pre-dosed him a few times, just in case, but it works far better for vaccine reactions (and teething!) than tylenol. It helps to reduce the inflammation (the source of the pain), so it helps in two separate ways for pain relief.
Hope he is better soon!