Really quick, you friend is not correct that things like dizziness, fatigue, and nausea are normal results of having sex. They can, however, be signs of illnesses (including mild things like the flu), so if you've had those symptoms for a few days and they aren't going away or are getting worse, it's time to check in with a healthcare provider.
Given that it sounds like you don't want to become pregnant any time soon, can I ask why you and your partner chose not to use a condom? Was it a matter of not having one? Being in a rush? Something else?