You say your fatigue may be due to stress and/depression.
Setting the smoking aside for a moment I would suggest that you perhaps are suffering from what is know as Reflux.
Acid will back up from your stomach into your esophagus and cause what is know as acid reflux or gerd. Depression and stress as well as smoking add to the cause and symptoms. Other cause's such as certain foods and medications will also effect or cause reflux. Using a pillow to raise your body and back in a more upward position may help lesson the symptoms. Over the counter meds such anti-acid tabs or Mylanta, Maalox are a few.
Your very young to be smoking and have immediate health related problems but that may not always be the case. It normally takes a healthy person years to develop COPD or smoking related problems unless pre-existing respiratory conditions exist. I would slow down on the smoking for awhile and see if things get better. It may be that with your stress level the smoking has induced the acid reflux.
If on the other hand if things do not get better within a few days time I would consult with a family doctor for examination.
I have attached a link for Acid Reflux and it's symptoms and medications to take.
http://www.diagnosishealth.com/gerd.htm
http://www.medicinenet.com/gastroesophageal_reflux_disease_gerd/page3.htm
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regards.
