First Ultrasound

My doctor said I don't need my first ultrasound until 18-20 weeks!! So I chose to do the ultrasound that will check for abnormalities around 11 weeks just to give me some kind of peace of mind everything is going alright as this is my first and I've had severe all day nausea and vomiting for the last week and just general upper stomach discomfort, feels like I have a bowling ball in there. I'm currently 7 weeks. History of twins in my family as my immediate cousins are identical twins.