About Three Weeks Ago I Was Out Walking My Dogs

About three weeks ago I was out walking my dogs and had this ache in the middle of my rib cage - kind of like a side ache but in the middle of my rib cage. I stopped and it went away, but it felt like something was still there. So, now I have this dull ache there, my stomach growls all the time, feel nauseated, and my upper back hurts. Any ideas?