I'm a little overweight and had my first ultrasound at 8 weeks, they thought I'd need to have it done internally, but we ended up getting all the pictures we needed so we didn't have to do it internally. Let them know about your concerns and that you want to try it externally first and then if you have to do it internally.
I recently had 1 , I was 9 weeks and it was external. I also had 2 dons before 1 at 7 weeks and 6 weeks both were external. For those 1 of those i was in the ER
It will most likely be vaginally because you won't be that far along. My first ultrasound was vaginal bit when I went for my 12 week scan it was external