Why github does not recognize my username in my commits?

You probably use a different email address for your commits, that you defined within the github settings.

On the one side you can define as many email addresses, that should be associated with you, as you like in your accounts settings under "Emails" on github.com.

On the other side you should set "your" email address in your git config

git config --global user.email "[email protected]"

The reason is, that git (it's not githubs fault ;)) uses email addresses as identifiers for commits. The name is only to display it, when requested.

Have you checked what e-mail address is associated with the commit message? I believe Github only attributes commits to you if the e-mail address associated with the commit is also connected to your Github account...

See Github's cheat sheet for information about how to add e-mails to your git config:

git config --global user.email "[email protected]" 

If you type:

git config --list

you'll see all your current git configuration settings.