Need a positive way to deal with stress?

Sometimes when my 4 month old has a bad day, and I get no sleep and he is crying non stop I get so angry. I would never hurt him or myself.. nothing like that I just get like so stressed I cry, and I just want to scream.. And I get really snappy and verbal with my husband.. I hate when this happens.. its not me. And sometimes when he is at work I am the only one here.. Any advise? I have tried setting the baby down in the play pen and letting him cry while I take a quick break.. but it doesnt really help because I know he is still crying, and I feel really bad.. Any other suggestions?