Body language/facial expressions

This may seem a little random.  I've been reading some material about body language, in the hopes that I might be able to improve my reading of other peoples body language - something I feel I'm very bad at.  Everything I've read seems to be assuming that you're capable of reading your own body language - for instance knowing what expression is on your own face without looking in a mirror. 

I can't.

I mentioned this to the person who is supposed to provide me with advice & her only response was "most people can".  She also said that she'd never heard of anyone not being able to read their own body language, & that was the end of the discussion.

I can't seem to find anything anywhere relating to this issue - am I really the only person in the whole world who can't do this?  Will I ever be able to do anything about it?