This is a difficult situation. The standard for diagnosis of syphilis using blood tests is to first do one kind of test called a "non-treponemal test" such as a RPR or VDRL test. If this is positive, then a second test, called "treponemal" test is performed to confirm whther the person has syphilis or the intial, non-treponemal test was falsely positive. If the treponemal test is positive, the diagnosis of syphilis is made and treatment provided. If the treponemal test is negative, as is probably the case for you in the past, then the intital test has been shown to be false positve and no treatment is required. False positve tests are more common in pregnancy.
If your husband's syphilis test is negative and you have had no other partners, the chance that you have syphilis is very, very low. Public health authoritites and many physicians prefer to err on the side of caution and to be 100% sure that the baby will be OK and therefore treat persons in your situation.
The issue ot whether you should be treated or not is something that you and your doctor need to work out. My guess is, based on your history, that your most recent test is falsely positve. This DOES sometimes happen in preganancy. Many of my patients in this situation choose to get the shots rather than fight things.
I'm not sure if this complicated explantion helps or not in this difficult situation. I hope so. EWH