Low libido can be a number of things, I'm a woman, but observing my boyfriend helps me understand why it happens in men. (Sorta) Low libido can be caused by stress or depression as your doctor has mentioned. However it can also be caused by not enough exercise, poor diet as well as low blood flow. Another cause could be that your currently bored with sex or life in general. Try some new things in the bedroom and outside! Low self-esteem may also be a cause.
Observing my boyfriend I have noticed that if he does not exercise enough he is hardly ever in the mood for sex. I have asked him to exercise more and we went from sex once or twice a month to twice a week. However if he slacks off on his exercise we fall back into the once or twice a month.
Normally he gets an erection many times a day but if he is working too hard at his job or worried about something he won't get any. It is healthy for a man to have several erections through-out the day and during sleep at night. It exercises the penis and keeps it healthy.
If you think you have having problems with blood pressure/flow try a dietary suppliment called fish oil (My boyfiend and I take it because we do not eat any fish). It has helped tremedously with my blood flow and his! Make sure that you are getting everything you need in your diet. If you are getting too much of something or too little (perhaps something very important you aren't getting at all), This may cause low libido because your energy level is just not high enough.
Hope this helps!
Tiffany
Forgot to mention my Doctors asked mevarious questions and said they doubted it would be a serious illness like I'm worried about because I'm not presenting any other symptoms they'd expect.