I wish I could give you a straight answer, but the possible answers are vast. How old are you? It's possible that the xiphoid process is simply developing, as it does with age. It's also possible that you're encountering re-mineralization of your bones and cartilage. It's possible you have H. Pylori/an ulcer or you may not be digesting the higher meat intake as well. Have you ever taken Betaine HCl? I would recommend doing that and seeing if your condition doesn't improve or goes away completely.

could be costochondritis. i developed it from prednisone and it sometimes felt like i was getting stabbed in the sternum. exercising was the easiest way to make it worse, so i avoided all upper body work for a while- likes months. the main thing that helped me was using boswellia cream. i would rub it all over my chest every day and that really relieved the burning pain.

also, you need to get an x-ray to diagnose this. there really isn't a treatment either. just rest.

Take a proton pump inhibitor like omeprazole and see if that helps. Medically, pain localized to x p is usu gerd or costochondritis but since it is brought on after meals rather than due to specific movements (lifting etc), its prob gerd.

Also just wanted throw this out there... make sure you're not having a heart attack. Its difficult to help diagnose without knowledge of your risk factors, age, weight, etc...