hi jennie,
i thought i'd share a short TRUE story with you.
a friend of mine experienced EXACTLY the same as you....2 failed ivf, tests after tests, which all came back clear, she had no problems, then they decided to come to terms with staying childless and went on holiday....next thing she knows she's pregnant with twins and in december had a boy & girl.
so don't give up but try not to obsess , i know its difficult but they say when your relaxed and least expect it, it will happen !!!!
good luck