Here's an old thread that tries to compare the two. https://www.medhelp.org/posts/STDs---STIs/Difference-between-herpes-and-primary-syphilis-sore/show/980040. The
main thing I took from that thread is that your sores showed up a bit too early for syphilis which usually don't show until around 21 days after exposure on average. From the CDC website:
"The time between infection with syphilis and the start of the first symptom can range from 10 to 90 days (average 21 days)." Here's the link in full, regarding transmission, symptoms, etc. http://www.cdc.gov/std/syphilis/STDFact-Syphilis.htm
Here's more info on syphilis https://www.std-gov.org/blog/chancre/
I've read chancres can last 3 to 6 weeks and then disappear.