IgM are the first antibodies to show, indicating a recent infection. Band 23 is highly specific to Lyme - it indicates that the Outer Surface Protein "C" of the Lyme bacteria has been found - or rather a reaction to it has been found in your blood. This means that you do have Lyme, as nothing else will cross-react to it.
You can read more here:
www.anapsid.org/cnd/diffdx/wb.html I am surprised that your LLMD has you on 300 mgs a day and not 400 mgs - but that may be because of your recent delivery of your little one. I would ask though.
Have you read through the "New to Lyme?" thread yet? If not, please do, it contains some important info about
taking Doxy, as well as symptom lists so that you can know what is 'normal range of things' that can be experienced with these infections. Things like pains that are intense one day and not there the next, herxing and how to detox to keep that at a minimum (as our bodies don't heal well when we are herxing) and more.