Have facial pressure on left side of nose and in my head round by my eye, nasal congestion and post nasal drip. it is not a sinus infection.any ideas?

Blocked sinus: This can be an inflammation in the nose or low grade nasal infection causing blo9ckage of the sinus openings. See an ENT doctor.

Likely a sinus issue: These symptoms do sound like a sinus inflammation. The fact that it's unilateral deserves an evaluation by an ent. Allergies or a sinus infection are possibilities, although both of these would usually give bilateral symptoms. May have a polyp etc on one side. I would take over the counter Claritin (loratadine) daily and go see an ENT specialist if it does not resolve after 3 to 5 days.