Hi I Had An Ultrasound On 12 Day.that Day Egg

hi i had an ultrasound on 12 day.that day egg size was 18 mm.docter suggst me for the hcg injection.on 15 day the egg size was 37 and it was not rapture.i had taken fertomid from day 5.i also had an ectopic pregnancy in 2013.now i dont understand whts the problm...plz help me?