I'm sorry you're going through all of this! I had a 3 year battle with (primary) infertility, and had all of the tests out there. The HSG can be very painful, I won't lie. I've had 3 of them in my life. I would take some motrin about an hour prior,if you are allowed to have motrin with the clomid...I forget. (I didn't have my HSGs during a meds cycle ever.)
Basically, the HSG is going to make sure your tubes are open. The first one I had neither tube was open and that test like to have killed me. BUT...I was not expecting to see those tubes blocked, so not only was it physically painful it was devestating emotionally which might have contributed to the pain. The pain came from them flushing that liquid in and a-my tubes were blocked so all that fluid stayed and was pressured into my uterus, and b-I had 2 polyps in there, so there wasn't as much room anyway.
The next one I had was after I had surgery to remove all the gunk from my tubes and uterus. This one was more frightening beforehand but less painful as both tubes were incredibly open! I also took the motrin beforehand that time!
The last one I had wasn't painful at all, really, although that one showed that I had one blocked tube. At that point I had no children and just figured well, it's going to be a long in-vitro path to mommyhood! I had moved from another state to IL where at least there is some mandated infertilitiy treatment coverage by insurance.
Less than a year after the last HSG, much to our total surprise, I got pregnant. And a year after my first was born, I got pregnant again. Go figure. We'll never know how I could go from being a fertility train wreck with all the issues I had (I had WAY more than blocked tubes) to 2 kids in 2 years, but I believe it was stress and how my body handles it. I'm just grateful for the outcome and I hope you have a positive outcome too.