Could my girlfriend be pregnant?

Well I'm sixteen and my girlfriend is 14, and we just started having sex around 3 weeks ago. We are always careful and always use condoms. She isn't on birth control. She was expecting her period on Monday and still hasn't got it. I thought maybe she is late because sex may have changed up her cycle, or her mind was forcing her body to think it's pregnant, because I've heard things like that before. We've also been very stressed recently. In addition to the missing period, she has other symptoms. It is normal for her to get headaches and have a sore back, aswell as dizziness and maybe some things I'm forgetting, and I noticed them on symptom lists. The abnormal sympto
s are that she's been hungry a fair bit more, she has a pink/ brown discharge, and she was nauseous today (although she might not have been eating well.) her areolas are normal as far as I can tell, but her breasts are sore. I think it's because she's due for her period, which I'm hoping this brown/pink discharge will turn Into.

Please help, thanks in advance.[/img]