Hi hope_29. Are you being treated by a Lyme doctor? Can you discuss this with him/her? I don't think a doctor would email you without having seen you and/or knowing your history.
Many Lyme doctors follow Dr. Burrascano's treatment guidelines. He lists recommended doses of Flagyl (Metronidazole) as "Metronidazole: 500 to 1500 mg daily in divided doses." You can find this on the bottom of page 18 at http://www.ilads.org/lyme_disease/B_guidelines_12_17_08.pdf Other antibiotic doses are listed there also.