Can you take cephalexcin 500mg for a sinus infection?

Nasal congestion: Get oxymetazoline spray for the congestion. Can use this every 4 hours for a few days to relieve congestion and possibly decrease swelling enough to get some air into sinuses. Nasal irrigations with saline to remove secretions and debris. Take tylenol or aspirin for the fever/chills. May need antibiotics, i.e augmenting, zithromax, avelox

Infection: It sounds like you are suffering from a respiratory infection. It could be viral or bacterial but hard to better know without understanding more, like duration. Antibiotics may be necessary, though Keflex isn't typically one of the more common one used: it may work for some. Good hydration, safe steam exposure, nasal saline spray, expectorants like guaifenesin, and steroid sprays like Flonase