Based on the information that you’ve provided, your respiratory symptoms, including the “tightness” you describe could well be secondary to asthma (aggravated by cigarette smoke) or a condition called Vocal Cord Dysfunction (VCD). Cold air can also aggravate either of these conditions. Given your young age and relatively minimal smoking, it would be highly unlikely for you to have COPD, even early or Mild COPD. The combination of a chest X-ray and a simple breathing test (Spirometry) would rule out the diagnosis of COPD, with almost absolute certainty. Such a breathing test, especially when performed both before and after the administration of an inhaled bronchodilator could also go a long way toward establishing the diagnosis of asthma or VCD. You should discuss this with your doctor. Such symptoms, as you have experienced, can also be caused by infection or a mass in one’s throat but the normal ultrasound would almost certainly rule out that diagnosis.
I strongly recommend that you, working with your doctor, make a strong effort at complete, permanent smoking cessation, when you return from your current travels. That would be a decision you will never regret. especially with your history of “feeling better” at times, in the past, when you have temporarily stopped smoking.
Your gastrointestinal symptoms are consistent with the diagnosis of GERD (reflux), despite the lack of improvement with Zantac and could be aggravated by the Dexedrine, as could a variety of lower intestinal disorders, including but not limited to Irritable/Inflammatory Bowel Disease (IBD). You may do well to see a GI Specialist for accurate diagnosis and complete resolution of your intestinal symptoms, both upper and lower intestinal in origin.
Good luck
Are you taking the dexedrine for ADD? That is what it is recommended for.
Dexadrine is a stimulant which, if you are anxious, would increase your anxiousness more so.
The tightness in your throat could be indicative of an upcoming panic attack. The fact you say valium makes you feel better would indicate my being on track with that since valium is used to ease panic attacks.
Nicotine is also a stimulant, so it appears that you might be having anxiety issues. When a panic attack starts it can feel like you have a lump in your throat, like a person gets when they are starting to cry. This is a bronchiol spasm.
You might tell you physician about these symptoms and ask him if it isn't a panic attack and he might prescribe something different to eliminate them altogether.
Just my thoughts...