I was exposed to someone with covid about 8-10 days ago, i tested negative on wednesday but since then i've developed a fever and tight chest with yellow/green phlegm slightly speckled by blood. my blood oxygen is between 94-97% and my temp is 38.

Acute bronchitis : This sounds like it could be like your bronchitis or even pneumonia. Even though you tested negative for corona for an exposure 8 to 10 days ago it is still possible that someone else might have infected you. I would repeat your corona testing in another five days and would seek medical attention for the lower respiratory tract infection and you probably have.

COVID 19: You could have a number of pulmonary conditions that could be due to different infections. It is possible that COVID 19 was a false positive. Rest, hydrate, quarantine & eat healthfully. Consider use of acetaminophen, saline for nasal irrigation, decongestant or cough syrup. Get urgent care for difficulty breathing, blue lips or face, marked persistent chest pain/ pressure or new onset confusion.