I too find stress sometimes hard to deal with.
People say cardio helps, which it certainly can do. But it's easier to use it as a preventative mesaure than as a method of combatting it in the short term: I find running during stress means running with tense muscles which can be difficult.
Yoga definitely helps me and, although, I've never tried it, I'm sure meditation has similar effects. My boyfriend says it's great.
When I'm stressed and tired, I find I become erratic and lose concentration: I think forcing myself to do things more slowly and in a more considered manner would probably help: I'm trying it out today.
Hope you're keeping it all under control