OP, one thing is for certain. If you keep telling yourself you can't, can't, can't, you will never be able to. The mind is a powerful tool. You can use it for you or against you, and right now, you are falling square in the latter category. Maybe your therapist can give you some insight on the power of positive thinking. It could go a long way toward helping you reach your goals. I come from a family full of medical issues and depression. Sure, I'm well aware that it's easier to give up, to not take responsibility, to just say "I'll never be able to do that, so why try?" But is that really how you want to live the rest of your life? My sister has often asked me how I am able to do all that I do, and the answer is simple. I don't give myself another option. I just jump in feet first and DO.
So I'll try agian-I've got the strength in me somewhere. I just need to work on bringing it out, even if it takes a long time.