You need to clarify your diagnosis with your doctor. Those are not allergy medications, but GERD meds.
Zantac (ranitidine) is an H2 blocker which is a type of antihitamine, but it is generally not very effective for respiratory allergies. Nexium in a proton pump inhibitor.
Deepending on how bad your GERD is, the combination is quite common. I take ranitidine and Dexilant (also a PPI). For break through reflux, I take Mylanta or Rolaids. I have also been diagnosed with bile reflux and take a fourth medication for that.
It is best to manage GERD with diet and life style changes if you can. I also take a digestive enzyme and probiotic. I took a double dose of the probiotic for about 2 - 3 months a while back after taking a lot of antibiotics. That got my reflux under much better control.
Let me know if you have any more questions.
Take care and feel better.
Both these medications are for relief from GERD (gastroesophageal reflux disease) and post nasal drip or mucus congestion has GERD as an important cause. Also eat small nutritious meals at frequent intervals instead of a heavy single meal. Exercise frequently and take your dinner atleast 2 hrs prior to bedtime. Also raise the head end of the bed by 2 blocks.
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.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.