First of all, relax. The more freaked out you are, the more freaked out they are - and that certainly doesn't help anyone.
If you haven't yet, cleanse it with peroxide. If it were some where on the body without lots of hair, I would suggest that triple abx ointment also be applied with a bandaid. But since it's his head, it's best not to try to put the abx ointment on it.
You can get him in to a LLMD, but I don't think they will do anything unless he has symptoms and/or a positive test.
If you wish to use herbs, Buhner says to start them on astragalus immediately:
buhnerhealinglyme.com/herbs/astragalus-for-kids/ I was using astragalus for prevention and just pulled a tick off of me last night, so I raised my dose to the 'full strength adult dose' to hopefully ward off any symptoms, so I'm waiting and watching.
Please do let us know what you decide to use and how he's doing!!