Well, back pains and nausea can occur pretty early in the pregnancy, but I've never heard of running a high fever. However, it is possible to run a low grade fever early on in a pregnancy..but I think those symptoms would last longer than a day. My guess is that she just got sick. But by now it would be late enough for a pregnancy test to show up, if she was pregnant. You can either buy one or find a crisis pregnancy center nearby--they usually give them free. If this turns out to be a false alarm, all the better. Take it as a huge warning--you're getting off really easy! Don't have sex until you are ready to raise a family. Once she is pregnant, you can't really undo it: even abortion doesn't "cancel" the pregnancy...it's never quite the same after. Someone will be gone that you never even met. There is no perfectly safe way to prevent getting pregnant except the obvious..stay out of bed. I know it can be particularly hard for guys to resist this, but it can be done! ;-) But if she is pregnant, I know you are man enough to stick with her and help her with it! You're both in this together...remember that. A baby, and from here on out it's not about either of you anymore. It's about your family and sticking together. You both have a lot more in you than you think!