It is like a burning gnawing paid under your breastbone with maybe some chest pain, shortness of breath?
Could be acid reflux or the start of an ulcer.
See if antacids help and avoid anti-inflammatories (eg aspirin or ibuprofen), spicy and rich foods and smoking.
Maybe best not to overeat as well though in ulcers the pain can sometimes be relieved by eating.
Could also be a pulled muscle or something like gallstones.
If the pain isn't helped by antacids or gets worse or you get any jaundice (yellow tinge to you) then go see your GP, any vomiting or blood in your poo, shoulder pain or fever then go to A&E.