I checked my blood, everything is fine doctor said, but i feel weak and loose energy quickly when i do physical work. anxiety, lack of concentration.

Many possibilities.: There are innumerable medical, nutritional and emotional conditions that include being tired as a symptom. These range from simple issues to those far more complex. A good checkup and blood testing would be a good starting point. Do you sleep well, or could this be a sleep quality issue? Could this be depression as well as anxiety? How thorough was the blood test?