Depression and anxiety are the main reasons for this.  Those of us who have experienced it understand what you are going through and have been able to work through it so far.  There is medication that will help which doctor can prescribe but, better yet, see a psychiatrist who is trained in helping you deal with this both through therapy and medication. They are doctors with additional training in psychiatry.  Make sure you are seeing a certified psychiatrist and not someone with lesser qualifications. 

That being said, my email is in my profile and please contact me.  Believe me, I know exactly what you are going through and I wouldn't wish it on my worst enemy.  Take care, my friend.     .