thanks for ur query,
after all the test u have done are normal ,u prefferably should get ur husband semen analysis
done.u need to undergo a small surgery -diagnostic hysterolaproscpic surgery , which would give information of the interior of ur uterus
to know the environment for ovum implatation , tubal patency ,important thing for the ovum and sperm to travel and unite to form an egg . this will give a better guidence in finding out the fault .
take care and ask ur gynecologist about the hysterolaproscopic procedure.