I don't think it's a girl thing. Men can be like that as well. So it's a mind set. See the "brighter" side of things and try to focus on the kind of things you say. When you want to start saying something, try to decide if it's positive or negative. Then decide if you actually want to say it and if it's important to say it.
Why are you being sexist? Guys complain just as much as we do - in their own ways. And you can stop it, if you have self control - which you do, so don't act like you dont. If you actually think you have a real mental disorder, then go see your doctor. Otherwise, you can stop acting that way.
You probably complain a lot due to not having a positive attitude.
If you are negative you will always find something to complain about.
You most likely don't realize what you are doing because you may have
grown accustomed to being so negative all the time.
Others may hate this since no one wants to be around someone so negative.
Don't you think you would too be annoyed by someone who is always complaining?
You can stop it simply by changing the way you see things.
Instead of looking for the bad in things, look for the good.
Try to look more on the bright side and if you do happen to see
something negative, don't complain about it, try to do something about it.
You'd be surprised how far being positive can take you [: