I'm so sorry, Evanston! I do hope that you get this under control soon! Do be sure to stay very hydrated, and eat foods/liquids that are very easy to digest too.
ILADS says that treatment for RMSF is the same for Ehrlichia: "Standard treatment consists of Doxycycline, 200 mg daily for two to four weeks. Higher doses, parenteral therapy, and longer treatment durations may be needed based on the duration and severity of illness, and whether immune defects or extreme age is present. However, there are reports of treatment failure even when higher doses and long duration treatment with doxycycline is given. In such cases, consideration may be given for adding rifampin, 600 mg daily, to the regimen."
www.lymenet.org/BurrGuide200810.pdf (page 25)
Doxy and Mino are both tetracyclines, and Mino has better penetration of the BBB.
And.... we've reached the end of my abx understanding. LOL!
But, I do hope that you get this under control soon or that you find alternatives if you can't. Please do keep us posted!