Can I have the flu with congestion / sore throat? I am very sore all over, extremely weak, and have a fever of 100. No nasal congestion or sore throat

Yes. Flu affects people in different ways with some even having gastrointestinal symptoms. If flu is going on in your community, then it is likely the cause but do note that many viral infections can lead to similar symptoms. If the symptoms started less than 48 hrs ago, a Rx flu drug may hasten your recovery.