This is Dr. David
it sounds like you most likely have strained muscles or intracostal muscles between ribs below your left breast with your coughing from your infection.
you can use heating pads and ice packs on this area to see if that helps the pain.
you can use over the counter NSAIDs like ibuprofen or naproxen sodium with food in your stomach to decrease muscle inflammation pain.
you can use your morphine patches and tramadol as well.
if you continue to have pain, you may need a rib xray or CT scan to check for mild rib fractures.
I would start there.
let me know if you have other questions.