V.J.
Not trying to frighten you, but aside from the obvious possibilities of allergies, a cold, bronchitis, etc-- you might consider getting tested for Valley Fever. Chest pain, cough, and lethargy are common symptoms of it and you don't necessarily have to have a "fever" for the diagnosis to fit. Valley Fever can present itself in a number of different ways and symptoms can be anywhere from very mild to sudden and severe. It's a simple blood test to find out and might be worth considering if your symptoms don't go away in a reasonable amount of time with OTC meds and rest. Best wishes-- I hope you're feeling better soon.
http://www.mayoclinic.com/health/valley-fever/DS00695