I Was Put On Amoxicillin (liquid) For Sinus/ Throat Infection.

I was put on amoxicillin (liquid) for sinus/ throat infection. Now my in have pain in my stomach area, high between the ribs. Could this be IBS or Gerd. I have both,but they have been under control until taking the amoxicillin 2 days should. Just talked to the doctor today and was told to take Zantac but no relief.