If there was a dangerous amount of water in my lungs, i would be constantly coughing wouldn't i?

Context?: While generally water or fluid in the lungs is no well-tolerated (like in near-drowning), even small amounts of fluid can be dangerous even without causing coughing. For instance, in parapneumonic effusions, a tiny bit of fluid can harbor dangerous bacteria. You seem rather young to be afflicted with pneumonia, so I am curious about the context in which you got fluid in your lungs. Makes a diffnce

Yes: Otherwise normal 18 year old lungs would respond to excess fluid by symptoms of coughing and shortness of breath.

Coughing: few things cause coughing: 1) bronchitis- from smoking/virus/bacteria/allergens; 2) post nasal drip from sinus or nasal issues; 3) Acid Reflux-no sputum usually. just dry, annoying cough; 4) medications-also dry; 5) pneumonia-usually would be sicker with fever, fatigue; 6) water in lungs-aka pulmonary edema-liklihood of having this at your age is VERY LOW. still recommend u get it checked