I also recommend you advise your sexual partners of your Syphilis status so they could also get tested and treated if necessary.
Your post is a bit hard to understand but I will try to sort through it:
You mentioned that you were diagnosed with Syphilis since February this year.
You also stated that you were treated with Penicillin.
Since your last checkup, your doctor said you have a 'new' infection?
Or am I misreading your post?
If you hadn't had sex since your diagnosis but you were treated for Syphilis, then its possible that the dosage you had was not high enough to eliminate the bacteria... or, it was simply misunderstood because the Syphilis tests would be reactive for a LONG time after treatment.
It takes about 3 months after initial treatment with Penicillin to see a 4x drop on the RPR and other measurements.
Also, many people continue to test positive on the syphilis test even after successful treatment because they still have antibodies for it in their system - but the bacteria WAS successfully eradicated.
Penicilin is the only recommended treatment during pregnancy.
Which stage of Syphilis were you in?
There are 4 stages through which Syphilis goes through:
1. Primary
2. Secondary
3. Latent - non infectious and asymptomatic but the bacteria still continues to damage the body/organs - can last for decades
4. Final stage (may or may not develop after latency period)
Syphilis treatments vary depending on the stage the disease was in.
For the first and secondary stage, a standard dose of Bezathine Penicillin G (24 million units), 1 intra-muscular injection is used.
For the other 2 stages, 3 Penicillin IM injections are used (one injection every week).
In case of neurosyphilis, the treatment that is used is 10 days of IV Penicillin (and I think this is followed by 3 weeks of IM injections- 1 injection per week).
The only recommended treatment for Syphilis when a person is pregnant is Penicillin.
Other drugs are not used due to the possibility of them causing abortions.