Personal question time: How do I stop being so angry all the time?

First and foremost: I know this is not a viable substitute for professional help. I’m looking for a psychologist that I can afford, but in the meantime I need to find something to mitigate the problem.

That said: Yesterday, after an argument with my girlfriend I realized I really have a big problem with anger. I wouldn’t say it’s undirected, per se, but I realized that it mostly builds up during the day and spills out with my mother and girlfriend (I don’t think I need to mention that I’m very ashamed of this particular detail.) for any stupid reason. Now, I realize it’s probably partly because I’m an only child and I’ve become very self confident in the last 4 or 5 years, which has had a big part in making me act like a twat in the past, but that can’t be all.

The big problem is that i don’t realize when I have snapped until after I calmed down, which comes about too much time after I’ve already done the damage. I need to learn to prevent this, but I don’t really know how.