Talk to Gynecologist on Inquiry Related To Medicine In Pregnancy

I am 9 weeks 4 days my first pregnancy..I got vaginal bleeding on 30 april and still have blood group is B- and my husband blood group is O+ doctor prescribed my Anti D injection for to her this bleeding may be because of blood ultrasound is fine and baby is healthy and active..I wanted to know is it the right time to take Anti D injection...I heard that this injection is given on 7 month of pregnancy.