Hi @emilymahomie, I echo the welcomes and I am sorry to hear about your struggle with GERD, Celiacs, food allergies and anxiety. That is an awful lot to deal with at any age, let alone being a young woman starting college. I agree that it would be wise to seek a second opinion from a cardiologist to make sure you aren't having any heart issues, however, did you know that Nexium can be known for causing stomach pain and rapid heartbeat? It can also cause a large influx of gas and pressure that builds up and can rise into your chest making it feel like you are experiencing chest pain. I was on a proton pump inhibitor as well and my symptoms (much like yours) were a cause of over treatment and under treatment with the medication.
The following article mentions, "Patients should always speak with their doctor before stopping Nexium. Stopping suddenly can trigger a “rebound” effect. This can cause the patient’s condition to return. It can sometimes be worse than the original problem."
– Nexium Side Effects: https://www.drugwatch.com/proton-pump-inhibitors/nexium/
Has your gastroenterologist suggested an alternative to everyday treatment? Perhaps every other day or four times a week. Using it for longer than 14 days at a time can cause inflammation of your stomach lining.