Thin uterine lining

I just had my first IUI on friday and the wednesday before that, I had an U/S and the dr said my uterine lining was a little thing - it only measured at 6mm. he said it should be above that but never gave me a specific # as to what it should be. He put me on estrogen 2x a day. It is now a week later and i went in to see where my uterine lining was and it only measured at 7mm. He said that # is fine and then told me good luck on the blood test i will be taking next week to see if I'm actually pregnant. That was it. HOwever, i just have a bad feeling about that because i read that it should be at least at 9mm or more. Has anyone else been in a similiar situation? Does anyone think implantation can happen for me with my lining being only at 7mm? I'm still taking the estrogen and I'm also taking progesterone suppositories to support a possible pregnancy. I'm assuming the uterine lining is thin due to the clomid i took but who knows because i never got it measured before.  I feel the exact things i've been feeling every other month i don't get pregnant so i'm a bit discouraged. I have cramping etc. I know it's way too early to be able to feel if your pregnant but i'm still feeling down about the cramps since i've gotten them every other month too.