On/off stabbing pain on various areas of chest & chin, belching and churning stomach after meals. Is this due to stress, heart or stomach issues?

Unlikely your heart. Given your age and the way you describe the symptoms, this is unlikely to be your heart. It is much more likely due to gerd, which could be provoked by the Ibuprofen and amoxicillin. You could consider taking Tums and Pepcid (famotidine) for a few days and see where that gets u. Also, you could switch from Ibuprofen to Acetaminophen for pain. Good luck.