I just discovered MDLinx, a website that provides scientific articles on many different diseases and conditions.
If you are a serious hypochondriac, as I am, I'm sure you will have sufficient medical understanding to find this site very useful. You can search on various types of illness and read either the abstract of the study or the full report, depending on the level of your interest. Sometimes the full report will require a subscription to a medical journal, but even knowing a study exists may be of use, since you can refer your doctor to the study if you think it might help them with your condition.
As a serious hypochondriac, I feel you, the patient, must be well-versed in your illness, or in the possible causes of your symptoms, before even going to the doctor. Doctors are so busy nowadays that many do not listen to their patients' symptoms carefully enough, and if you have one of those doctors, you want to be sure they test you for whatever you think you might have, because otherwise they might miss something!
I am very fortunate in that I have found doctors who are willing to listen to me, and will actually address my concerns, by either explaining why something isn't necessary, or else agreeing that the concern is valid. But many people are not so lucky, and if you may be dealing with something serious or life-threatening, you don't want to take a chance with your health.
Naturally there are some doctors that will not take kindly to your suggestions or questions. But I feel a good doctor would agree that "An educated consumer is their best customer" as the Syms ad goes.