Follicle cysts and thin endometrium lining

Hi Dr.,
Though I have two children, ages 8 and 4, my husband and I are struggling to have a 3rd.  It began with discovering an ovarian cyst that we cleared up with Yaz.  Then, the dr. prescriped letrizole and everything looked super, had two great eggs and a lining of 7 mm.  Administered Ovidrel, but, lo and behold, it didn't work, and I had cysts again.  Spent another cycle on Yaz.
Now, I am on CD 13.  Took Letrizole for CD 3-10, and had an U/S on Day 12...which revealed an oblong (but large) follicle, and another good sized follicle.  However, the good dr. said my lining was only at 2mm.  He told me to wait until CD 14 to take Ovidrel, and he said he had high hopes.
I am as scared as ever.  I have read that this is too thin, and chances of miscarriage are great.  Will the lining increase?  Also, is an oblong follicle a bad way to start (since he said it wasn't normal).
Is Letrozole causing thin lining as does Clomid?  Or what is going on with me?  It seemed so easy 5-8 years ago!!!
At what point would you recommend taking the next step?  What is the next step?
I feel like the more I research, the more pessimistic I get, even though the dr. still sounded optimistic!
Thanks!

[trying_hard_for_number_three]

Oops, thought I was writing to the dr, and here I am posting one billion messages to the same forum.  Sorry about that...as you can tell, I am very nervous...
So please ignore all the other ones written by me...they tell the same thing!  haha!
Good night.