Your sense of self comes from the information surrounding you as your grew up.
As a child you not only pick up the words constantly used by your parents you also pick up their way of thinking.
Then when you go to school your friends will have bearing on how you see yourself.
If your parents responded to every crisis with self pity and great drama then it is likely you will do the same.
If your parents responded to great drama by insisting that everyone just behaves as normal as possible then you will be a calm person under difficult circumstance.
You can even see owners character influence in their dogs based on whether the dog has a calm, happy nature or a frazzled, over excited one.
Okay so how to change your negative thoughts into positive ones? Change your friends.
If they are like you and consistently negative with whingeing personalities, they have to go I'm afraid...
or indeed join you in making an effort to change.
Stop the negative chatter going on in your head as soon as it starts.
Replace it with a positive thought EVERY time and it will soon become a natural habit.
Watch the information that you allow into your home.
Magazines, the TV you choose to watch, the books you read.
Make sure they are a positive force in your life from now on.
Often these sources of your information are wrapped up as entertainment so it is easy to miss how damaging they really are to your psyche.