I feel sick but can't pinpoint what's wrong?

Okay so for like 3 days I've felt crappy but there's nothing specific I can put my finger on. No throwing up, no stuffy nose, no coughing, etc. My body just feels super weak and I'm pretty tired (even though I've been getting normal amounts of sleep), and I've been pretty nauseous (but no where near throwing up) as well. I have a lot of very important things to do starting tomorrow through Monday (graduation and the following festivities) so I'm worried that I'm sick/am getting sick. Has anyone ever felt like this?