Sex drive. That depends upon why it left in the first place. If due to stress, resolve the stress. If due to an infection, get the infection treated. If due to relationship discord, repair the relationship. When the reason is unclear, it might be a good idea to have it evaluated by a doctor. Herbal supplements ("natural" meds if you want to get technical) such as tribulus may be of some help.
Sex drive. With the help of your doctor, find the cause & treat that.
It depends. Getting your sex drive back depends on what has caused you to lose it in the first place. Possible causes are relationship stresses, personal conflicts, depression, anxiety or medical issues. You might want to get a medical and mental health evaluation to understand what is causing your lack of sexual desire.