I just had this procedure done on April 16th and then again on the 23rd.
It did not hurt a bit the first time. They warn you of potential bleeding and cramping after but I had none of it.
The second one was a bit painful - a different doctor did it. I had a little bit of cramping after.
Anyway, they do it to look at the uterus - in my case they wanted to make sure that its shape did not cause a pregnancy loss.
Good luck! Hope this is helpful.