Syphilis False Positive

I donated plasma in February and I received a notification that the preliminary testing that they run came back reactive for Syphilis. I went back and did a blood test for further testing and it came back negative. I read a few articles that said that there could be other infections or diseases causing the false positive. Has anyone ever had this happen? I want to know why it came up positive to begin with but I’m not sure what to do. Any suggestions would be greatly appreciated! 

I have heard if such but also check again. The doctor is suppose to let you know hiw often to recheck yourself