16-year-old female with severe nighttime cough: What to do?

Difficulty in breathing, production of mucus and chest congestion could be a result of a respiratory infection or an allergy. A pulmonologist should be consulted to diagnose and treat the condition.
 

Pleural fibrosis results in thickening of the lungs lining and further development of breath problems and other symptoms. It may occur as a result of several different things like being exposed to asbestos or being infected by a certain bacterium or virus. I will recommend you see a pulmonodigist who can assess the exact condition and recommend a proper treatment plan.

Your symptoms suggest postnasal drip. It's cause­d by nasal mucus draining down your throat, triggering coughs, throat-clearing, eve­n vomiting. You feel like bre­athing is hard and need to spit freque­ntly. Staying hydrated and using a humidifier could provide re­lief.

When you lay on your chest and it feels hard to get air in, that could be from anxiety. Anxiety also makes it difficult for people to sleep well at night.  You can learn how to control your breathing when talking about it with them and other ways of calming down too if they know about it. Try doing things before going to bed like making a routine so that every time before sleep you will make sure that you get into bed more easily also practice good habits around sleep like not watching any screens an hour before bedtime because they keep awake longer which means fewer hours spent resting. If these symptoms stay or get worse then maybe it's time to see the doctor and tell them what’s been happening.