Generally, it is indeed correct to have your back to a wall when you are working.  BUT, you need to first analyze what kind of work are you doing AND what is behind that wall behind you.  

As you mentioned that behind you is a door and in front of you is another door I opine that you are finding it difficult to finish and/or concentrate on your tasks.  This is because you are in a position that will "absorb" chi coming from both directions.  

The key to effectively handle such a circumstance is to realize that feng shui is just a part of the solution.  Note that feng shui tells you what would be the result after doing an action.  Hence, martial arts or offensive action and medicine or healing are the other 2 parts.  How do you apply this to yourself to solve this problem?  Take note of the energy healing subjects shared in this forum.  That's what I apply and teach to those I assist in their problems given their limited options and resources.  Cleanse yourself often - especially if your work involves a lot of stress and handling of other people's sickness and/or problems such as being a medical worker, lawyer, policeman, etc. - and find time to renew your energies - which is why you need to do something worthwhile during your day off.

You can also use plants, crystals and other remedies but those need to be something you are attuned to.  Meaning, if you don't like gems then don't use that as a means to aid you in solving your situation.  It has to be something that you like and could understand.

Hi
In the book I have it recommends having your back to a wall and not have your back to the door - but it says if your desk is against wall with back to door a mirror can be placed above desk so you can see if anyone enters