My husband and I had four miscarriages before doing our fertility testing. Like you, all came back normal. All our miscarriages were what is called a blighted ovum, a "fluke" condition in which the egg is fertilized, it implants, but no baby forms in the sac. I also had a Hysteosalpingogram, to determine that my tubes were open. Good there too! Again, no reason for what was happening. Very frustrating!
What helped me was that I used the Fertility Awareness method to get to know my body. It helps you to see if you are ovulating, and when, and other things to determine when you should time intercourse. I have gotten to know the exact day I ovulate and/or when I will get my period. In fact, since I NEVER have a 14-day cycle, I was able to tell my OB when I was REALLY due to have my daughter last August, instead of him going by the Pregnancy Wheel. He would have thought she was LATE and possibly wanted to induce or due a C-section unnecessarily.
I think if your doctor is recommending the IUI and IVF because of the endometriosis, then perhaps that is ok. However, if you don't even know what your body is doing, how can you treat the unknown. If you are not ovulating, then that is a different story. I have friends who were not ovulating and have used Clomid with great success. Again, the Fertility Awareness method can help you determine these things, if you wanted to try it.
The book that teaches it is called "Taking Charge of Your Fertility," by Toni Weschler. Best of luck, and don't worry, it is only a matter of time.
A.