I had a HSG this past Friday and it wasn't so bad. It might have lasted about 10 minutes and doing the procedure, I got what seemed like a bad menstrual cramp. After the procedure, I had spotting that night and mild cramping but by the next day, I was fine. My advice would be to take some ibuprofen before your procedure. I took 4 (800 mg total). I was really nervous going in for it and when it was over, I was relieved it wasn't as bad as I was thinking it would be.
With the Clomid, I haven't had much side effects. Maybe a little more moody but not bad at all.
Glad to hear your doctor is being proactive and hopefully you will get good results. I am really hoping it does the same for me as well.