Hi there, I had my HSG (after over 2 years of TTC) two weeks ago. Just coming to the end of my tww afterwards.
I would recommend you do lots of research about what to expect and follow the advice of your doctor. I found it particularly helpful to take some pain killers about 30 mins-1 hour prior. I didn't take antibiotics - thankfully, I don't think I needed to. I also found it particularly helpful that the radiologist who performed the procedure talked me through every single step as he was doing it. He was a stranger who I'd never met before until he walked into the room with my legs up in the air!!! But him talking through the steps really helped. I also made sure I could see the screen clearly - I made them move it around further for me.
Some women have no pain at all during the procedure, some have severe pain, so it is hard to predict where you will be on the scale. The pain I had was worse than regular period cramps - almost to the point of tears, but I believe that was because he was pushing through more dye to try to clear out my tubes. Apparently my tubes were blocked at the ends and pushing through more dye opened them up and allowed the dye to flow through freely. I also felt quite light headed afterwards.
The pain dissipated after the procedure but I had residual pain, cramps and bloating for a few days. I felt awful that night and the next day - ibuprofen helped. DTD was painful for about 10 days afterwards, worse in specific positions, but last time, it was fine.
Go in with knowledge about what is going to happen and I hope it goes well for you.