hello all ! saw an RE yesterday

sandy • Married for 4yrs ... to the best man in the world ❤️ Now waiting for my two little girls to arrive . 🤰👯 Love my life & the way my love has designed it for me 👫
Hello I'm 29 & #TTC #1. 
I was on clomid last month 50mg. Where I had one follicle 20mm. Progesterone 9. 
According to doc I did ovulate but didn't get preggo. 
This month took clomid 100mg. Yesterday I had my sonogram done in the morning and I've one dominant at 22.4mm. So far it was with my obgyn. 
Saw a new RE yesterday afternoon & since I'm at the right time he asked me to come tomorrow i.e Saturday for another sonogram... 
hopefully he wants to do the trigger and <a href="https://glowing.com/glow-fertility-program">IUI</a>. 
I would like to knw more about this whole process . Pls someone make me understand what's going to happen. Is it painful or is it normal ? Is HSG must before <a href="https://glowing.com/glow-fertility-program">IUI</a>? 
Thankyou.