My girlfriend and i had sex (condom) on october 6. she had her normal periods on november 2 and december 6. she's usually late. she can't be pregnant?

Possibility is slim: Since protection is used, although not 100% safe, best way to determine if indeed your girlfriend is pregnant or not is a home pregnancy test. and of course, her primary care physician.

Pregnancy possible: It is still possible that she is pregnant. Condoms are 98% effective in preventing pregnancy if used properly. She needs to do a home pregnancy test or see her doctor for a pregnancy test.