My husband and I were told by my doctor at my 8 week visit that we would find out the sex of the baby in 8 more weeks (2 more visits) However at our last visit (12 weeks along) we did not receive an ultrasound and our doctor told us that we do not have to get an ultrasound every time it is just when the baby is at a different stage in growth and they just need to check for any complications. She then told us we would not receive an ultrasound for another two more visits. I am at 4 months and when I have my next appointment I will already be at 4 1/2 months and still have one more visit to go. I know at many other places they can already tell what the sex is. Can I make them do an ultrasound because waiting till I am 5 1/2 months seems a little far fetched to me.

You should be able to request one, just be aware that it may cost extra. Most insurance companies will only pay for it if it is necessary.

The sex of the baby is not determined until the 16th gestational week at the earliest, the best time to determine the sex is at the 20th gestational week. Sometimes the sex cannot be determined at 16 weeks, therefore most doctors and insurance companies prefer to wait until at least the 20th week.

You can try to make them do an ultrasound, but (not knowing your particular insurance) it may not be covered by insurance and may have to be paid for by you. This also does not guarantee that the sex will be able to be determined at this stage.

If it is the typical 2D ultrasound, sometimes it happens that the sex is never determined due to positioning of the baby. This is always a possibility too.

You can always ask for an ultrasound but more than likely you will have to pay out of pocket for the ultrasound. Most doctors wait to do an ultrasound at 20weeks. I know you are anxious to find out the sex of the baby but if you wait until a 20 week ultrasound they can be more sure of the sex and your insurance company will pay for it.
I am at 31 weeks now and I have only had 2 ultrasounds throughout my pregnancy. The first to make sure I was pregnant and my 20 week one. 20 weeks will be here before you know and you will still have plenty of time to buy the cute dresses or the cute baseball outfits.