Hi SNC,
No, 3 weeks is not enough abx to take care of a Lyme infection with EM and symptoms. You need to treat until all symptoms resolve - which is different for each person.
The easiest thing to read through that I have found and still comprehensive and accurate has been Dr. Burrascano's "Advanced Topics in Lyme Disease" paper. Dr. Burrascano is one of the founding doctors of ILADS, the only group that is interested in the science and clinical aspect of these infections, and helping the patients heal.
www.ilads.org/lyme/B_guidelines_12_17_08.pdf Unfortunately, we can't really tell you what to expect either, as it depends on a lot of things. Chances are pretty good you will experiences herxing though, so you do need to get started detoxing, eating super healthy, supporting any deficiencies that your body may have, and drink almost as much lemon water as you can force down. We cover a lot of this in the "New to Lyme? Start here!" thread that sits at the top of the forum.