What Causes Fever After Cervical Fusion?

Good evening, Tuesday, I had a cervical fusion from c3-c7. I've been running fever around 100 since tuesday. Today no Fever 86.7. I was so excited, finally on fever. Within 15 minutes I gos really sleepy and cold. Fever went to 101.7. Still having problems swallowing. Meds get stuck in esophagus. I just assume it will get better but this fever was scary. I woke up sweating and still haven't broken the fever. Don't know what to do.