(Anon, Aug 26th; original poster):
Thank you for posting back and updating us on what you found out!
Your information is very helpful for many women who have a late or missed period and negative pregnancy tests. It is important to go to your doctor to rule out any medical condition as the cause of late/missed periods, and I am glad that you were able to find the cause and receive treatment. It also helps to be a strong advocate for yourself, and this is difficult when you are the patient sitting there is a paper gown; bring a trusted friend or family member along to help with the questions.
I'm glad you are feeling better!