Testosterone would be the most common cause of low libido.
Other possibilities can include problems with the thyroid, as well as psychiatric issues like depression.
If the testosterone is in the high-normal range, this would unlikely be the cause.
I would consider a blood test to evaluate the thyroid as well as a depression screen by your physician.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Kevin, M.D.
http://www.straightfromthedoc.com