I had an internal ultrasound in the afternoon and it was a little bit painful/ uncomfortable at the time but nothing extreme. However, later that night from about 11pm til 4am I had the worst pain I'd ever experienced. I talked to my gynecologist about it and she said it would have switched on my pain receptors, which are obviously very sensitive in that area and used to chronic pain. I would advise you to take pain relief before and after (as regularly as you can during a 24 hour period) to hopefully get ahead of it. It wasn't until I was able to take my second round of codeine that I was able to get relief.

Yes my transvaginal ultrasounds are extremely painful