Everyone has to start somewhere in fixing things in life, so if its by logically looking at your pluses even if in reality you don't really believe them, then its a first step, the next would maybe be to seek help in how to manage, or try and change how you think, again easier said than done, but if it works for you (I know it doesnt for everyone) maybe cognative behavioural therapy would help, its a lot of hard work, but the difference it can make to your life could be great. Have you saught help from a Doctor at all?