Hi my name is XXXXXXX About a month ago my
need to check for sinusitis too...
I went through the details provided with diligence. You report that there is tightness in the chest, painful cough and it hurts to sneeze or breathe. You also complain that there is drainage in the throat with headache. Based on these symptoms, I'd consider possibility of allergic sinusitis with post nasal drip. And yes there is a possibility of lower respiratory tract infection; it may or may not be pneumonia yet.
Hence I'd strongly recommend you plan a visit to the doctor at the earliest. You need to be investigated. A complete hemogram, along with X-ray of paranasal sinus and chest cavity might be necessary. Based on the results of the test, you may need to be treated with antibiotics along with expectorant cough formula. Until then continue antihistamine medicines. Steam inhalation will benefit you.
Hope this helps. Let me know if you need clarifications.