What does it mean when I feel a knot in my chest through my back every night and it hurts when I breathe?

Lots of things. For any particular symptom like this it can mean so many different things that you really need to see a doctor in person to be evaluated properly.
Considerations...? Your pain may originate on either side of the diaphragm to produce your symptoms. Cough (dry or productive, with blood?), pleurisy, fever, nausea, vomiting, altered stool pattern, blood with stool, tenderness, distension? Do the symptoms "refer"elsewhere (to back, shoulders, chest, neck, jaw, arms)? Recent trauma, herniations? What is your age, gender, do you smoke, have heart/lung issues, stones?