Did the doctor test you? That's the only way to know if you have syphilis for sure.
It doesn't sound like it, though - syphilis isn't normally a bunch of sores. It is usually one or two round, painless sores.
What dose of doxycycline did he give you? Are you allergic to penicillin? Are you still with your girlfriend? She needs to test for syphilis. If she is negative, you probably don't have it, unless you've been with someone else. Even if you aren't together, letting her know is the best thing to do, since untreated syphilis can have very serious complications.
If your doctor didn't test you, go ask for a test. This is really important, because to know if you are cured, they will do another test later and look at the numbers.