I have all the symptoms of syphilis but the test results came back negative. What could I have?

Needs evaluation. The basic test for syphilis is calked an rpr. It is very sensitive meaning a false positive is rare. If you know you have been exposed then get retested. The symptoms of syphilis vary widely and can often be confused for other disease. Because of this syphilis is known as the "great imitator." see your doctor to evaluate what other tests for other diagnosis should be considered.
Prob not syphilis. This depends on the meaning of "all the symptoms", and when you might have been exposed. If your last possible exposure was more than 6-8 weeks ago, then the test result rules: whatever symptoms you have aren't due to syphilis. If it's been more recent and you have a non-healing sore at a sexually exposed site (genital, anal, mouth), keep working with your doctor and get re-tested. Good luck!