EMERG in pain after Letrozole/IUI treatment!!!

This is my first treatment cycle. I started Letrozole 5mg on Day 4. On Day 4&5 I started getting extreme back and abdominal pains I almost went to the hospital. But they lowered my dose to 2.5mg for the last 3 days and I felt better. Then I got my trigger shot on CD17 and did my IUI on CD18. On CD21 I was in extreme pain again and went to the emergency room and they gave me morphine and did ultrasounds. My doctor thinks this was me ovulating. I don’t know why I would ovulate 4 days after the trigger shot or why ovulation and Letrozole would case this much pain. Has anyone ever experienced this!?!?