I think my boyfriend is getting a fever. He feels lightheaded, nausea and his face feels hot. What can it be?

Viral syndrome. He is just starting a fever correct? Sounds like acute viral syndrome, which could be caused by any of common airborne viral pathogens. Focus on hydration, rest in bed, and keeping him comfortable. Should take otc analgesics to keep his temperature down to prevent dehydration. If he has high fever, chills & body aches, it can be a flu. It can be treated with tamiflu (oseltamivir) if within 48 hours of onset.