No sensation in clitoris

Patient: Hi,I am a 40 year old woman, no children, happily married for 17 years. At the moment I am quit satisfied with my life. I love making love with my husband and our sex live has always been good. However, since a month or so I have completely lost all sensation in my clitoris.I feel quit desperate. I tried everything from masturbation to using the shower head, but there is no feeling whatsoever. In addition, my vagina is dry. I do not think I have a lack of libido, cause my heart and mind desire sex. My body just does not respond. I am not ready for a life without sex. I do have some nerve pain in my lower back, not radiating to my legs.What could cause this and what can I do about it?