Estrace during IUI?

Has anyone taken estrace during their IUI cycle? Did it work for your lining? What CDs did you take it? I'm on my third IUI cycle and my lining is disapppinting every time. First cycle was 5.6 at trigger, second cycle was 6 (chemical pregnancy) and today at CD 9 my lining was only 3mm. My doctor has never suggested estrace but after reading I want to at least ask about it. I'm not sure what the downside of taking it is. This is the last IUI we will do so I want to make sure we can do all we can.