Pregnancy support pills do not necessarily cause birth defects, u seem to be panicking with out any cause as  ur betahcg has doubled in two days and hopefully it would continue  doubling in next few weeks as well. Also ,it is a parameter which has variable levels in different pregnancy with similar weeks gestation, depending on when the actual embryo was implanted . Better ways to judge the pregnancy status is by getting a scanning done now and at 12 the wk a dopplers Ultrasound done