Thin endometrial lining from clomid ????

Has anyone experienced clomid causing a thin lining ? Before I started clomid and early on w clomid I didn’t have a problem . How my lining has been 2.5, 3 3.8 the highest. I’ve been on clomid since July. Now after three failed iui and use this cycle of Premarin and Estrogen vaginally my dr wants to do a hysteroscopy in feb(which I’m refusing ). What about the clomid ? Why wouldn’t that be a cause . I had an HIS done in September - his words were - your lining is nice and thick , everything looks perfect. What should I do? I want a 4th iui before ivf but they won’t do ivf if it’s thin.

Anyone have this problem from clomid ? Ever use a different med other than clomid ?