On IUI, clomid caused thin lining

Nini • 39, TTC #2
I'm on <a href="https://glowing.com/glow-fertility-program">IUI</a>. First time. Today I had my ultrasound and dr said the lining is 6.4MM. Thinner than my regular cycle. It looks like Clomid caused the thin lining. Dr did not give me any medicine, just said if  I don't get pregnant this time she will use another med replacing Clomid. Anyone had similar experience? I'm so worried and frustrated at the same time.