** Thanks for contacting HCM with your health concern 1. Common antibiotics which are considered safe in pregnancy are penicillins, cephalosporins, and erythromycin and since you have to take the same for four weeks means that you are not allergic to penicillin and your baby is safe. PS. also penicillin group is in pregnancy B category which states that drugs in this category have no evidence of risk in present or later trimester. 2. please note that diarrhea is often associated with antibiotic use, so if diarrhea lasts for more than few days or contain blood contact your physician also penicillin use is associated with killing of healthy bacteria in vaginal tract which may cause yeast infection, if that develops [foul smelling discharge, irritation] consult your obstetrician for medicines to treat yeast infection which is safe in pregnancy. 3. Penicillin is the only recommended therapy for syphilis during pregnancy, alternative to penicillin is/are: tetracyclines, erythromycin, and ceftriaxone [remember not to use doxycycline as it has adverse effect on the baby and causes black staining of teeth ] PS. Following the initiation of treatment, in pregnant women, if they notice fever, headache, myalgias, early uterine contractions or decrease in fetal movement seek immediate obstetric care as after beginning the antibiotic therapy, a reaction called as Jarisch Herxheimer is common response due to an immunological reaction to the rupture of spirochete