All the symptoms that you have are due to sinusitis.Post-nasal drip (PND) occurs when excessive mucus is produced by the sinuses. The excess mucus accumulates in the throat or back of the nose. It can be caused by rhinitis, sinusitis, or laryngopharyngeal acid reflux. It can be enhanced or sometimes even caused by allergies.The stomach problems can be caused by allergies or it independently can worsen the symptoms.
Take plenty of fluids throughout the day and inhale steam as many times as possible. . Inhaling steam from a bowl of hot (but not boiling water) may help to soften, and loosen, the build up of mucus in your nose. You may also find that adding some menthol crystals, or eucalyptus oil, to the water, helps to ease your symptoms of catarrh.
Use an over-the-counter (OTC) decongestant combined with an anti-inflammatory analgesic (pain reliever) like Ibuprofen. However, you should not use decongestants for more than 5-7 days at a time.JKeep on taking OTC antihistaminics like benadryl or zyrtec.Some chronic cases may need oral steroids or steroid nasal sprays and antibiotics. These can be taken only after prescription.
If the symptoms persist then pls get it evaluated from an ENT specialist.
Hope it helps.Take care and pls do keep me posted on how you are doing or if you have any additional queries.Warm regards.