letting it go

I don't know how to let go of the stress from work.  I work on a very busy hospital unit, I'm just a secretary, but it is stressful and chaotic and exhausting.  It often makes me cry, but even more often makes me angry.  Angry at patients who are so non-compliant that they not only put themselves at risk but the staff, at my co-workers who never stop complaining about everything, at the administration that doesn't hear or doesn't care about the concerns of the floor staff, at myself for not having thicker skin and just doing my job without internalizing so much, and at my family who then demand so much of me after having spent my entire day being spun in circles.  I've always had a problem with being patient and I grew up in a household where the normal mode of communication was yelling and so I already have issues with snapping too quickly and speaking too loudly but over the past few months I have been becoming progressively more short with the kids.  I have a hard time even dealing with them on a day to day basis without raising my voice or out right yelling.  I hate it.  But I don't know how to stop it.  I don't know how to let it go at the end of the work day and go home and start over from a peaceful place. 
Today Phoebe told me that sometimes at school she likes to just play by herself because she like the quite alone time; that playing by herself makes her heart sing because it is calm.  I don't know if she needs that quiet time at school because that is something that I have failed to give her; a time here in her home when her heart can sing, or if it's just because she likes her own games over those that the other kids are playing.  Is she being strong by not catering to the others or is she pulling into herself because I've manged to fuck her up already.  Either way I need to learn to let the stress go, learn to be more calm, more peaceful.  I just don't know how.