if you are stressed out or have alot on your plate, this tends to happen. the best thing to do is to step back and treat yourself occasionally so that you actually have something to look forward to. this is my current problem. i am working long hours, dealing with difficult people, and a sick mother, constantly being a "yes man". at the end of the day, i am just exhausted and there is no time left to relax & reflect. i need to have 8 teeth pulled in a week, costing me alot of $$$, so this is keeping me down too. however, everyone else is so miserable and/or sick that they don't even notice and i seem happy in comparison to them. i am trying to work all these hours to make up for the 4 days that i need to recover from this procedure.
i used to look forward to weekends, but not anymore since i started working long days on weekends. usually, i find it easy to isolate myself when i am in a "snappy" mood. neither of my jobs require alot of social interaction, so this helps. i don't have a girlfriend(no time). if i did, the relationship probably wouldn't last long. i might scale back the hours i work a little bit and try to enjoy life more.
when i am in a bad mood, i just get really quiet. some people notice this and i just smile at them and say that "i'm tired". i try not to snap at people and haven't for a while. working out helps me blow off steam to the point where i am less likely to strangle someone.
i recommend this if you don't already do it.
i used to drink heavily, but that proved less effective over time. i just found that i was "borrowing" happiness from the next day. when the next day came, i was hungover and even more "snappy".