Can it be a sinus infection even if I’m not currently congested?

I’ve been sick for several weeks on and off with:
Sore throat and congestion (now mostly clear)
Post nasal drip
Extreme fatigue
Body aches/flu-like feeling
Low-grade temperatures around 99.9°F, usually lower in the morning and higher at night

Also, some of these symptoms like the fever went away and then came back again.

I also have a history of two sinus infections in the past year that required antibiotics.
Could this still be a bacterial sinus infection even though my congestion is improving? Would you get evaluated or assume it’s viral?