I have been at my new job for 2 weeks and just found out I'm pregnant.?

Should I tell them now, or wait till my 3 month probation period is up? So far they seem to be pleased with my performance and have said they hope I'm here for a long time. I work at night, and am on prescription meds for morning sickness, so I don't anticipate any pregnancy related tardies or absences. Can I be fired for being pregnant, especially because I'm still in the probation period? I live in Atlanta, Ga.