That's great that you do really like your job. You aren't worrying over nothing. Something is amiss, or you wouldn't feel this inadequate. It could be physical, or it could be psychological. The odds are much greater that it is a psychological issue. You could pursue this further with your doctor. You might ask your doctor to refer you for some counseling. It sounds to me like you aren't fully present to what's going on around you. That's very apt to be an anxiety issue. Just the very fact that you started this thread reveals you are dealing with anxiety. You sound like a worried person. Often that has to do with interpersonal issues.

Be open to the possibility that the cause may possibly not be physical. That doesn't mean it's your fault. It doesn't make you a worse person. It sounds like you lack confidence in yourself, and feel you are not at the top of your game. I'll bet something fairly important is missing in your life.