Me and my girlfriend have sex one day. That same day her ex boyfriend's new girlfriends say that she do not want him around her or her around him. She was very upset and wanted to do something about it. The next day she text me and say that we need a break. She puts things on Facebook saying that she does not feel like herself anymore. Could it be that she is pregnant. Or that the situation just made a mad and she need to think things over.

Drop this chick and find someone more mature & responsible.
When a woman says she "needs a break"it means one of two things,
1- Ï want to break up and don't have the guts to just tell you
2- I want to screw someone else right now, but I still want you in my back pocket
Either way, she is not emotionally mature enough for you or this relationship.
I hope you find someone worthy of your love. Good luck to you.