Obviously you should talk to your doctor about it, but as someone who's been dealing with different health issues/symptoms, it could be many things. The ones that aren't directly linked to heart issues, off the top of my head: various stomach issues (gastritis, GERD/acid reflux, h. pylori infection), vagus nerve issues (sometimes caused by stomach problems) that trigger anxiety and panic attacks, costochondritis, even things like mental trauma response can cause wild physical symptoms.