Keep grinding, once everything is done and dusted you'll come out stronger person. You've just had a major operation, which is quite a traumatising experience for an individual, so much so that it can affect a persons self confidence. Not many people are going through your pain and if they were to suffer the same fate as you they would probably fair worse.
I can definitely relate to the confusion; when I was poorly I wanted to know what caused me to be so ill, but not even the doctors can't give you a definitive answer, if they could, we wouldn't have this forum. So there is no point in dwelling on that question since it's not going to be very productive.