Vocal Cord Dysfunction or asthma or somthing other ?

[big J]

I am 25year old non-smoker who lives in a tropical climate I have hand a dry cough and tightness in my chest for about one year. I have no feeling of heartburn how every I have tried Antacid and they have no effect on the symptoms. I have had an EKG, echocardiogram and stress test done and the tests did not indicate any major problems. I also had a lung function test preformed and that was normal. I do have sinus problems due to chronic allergies and I am currently using a sinus rinse and have no or little current symptoms no postnasal drip.
My allergist told me it could be mild asthma or cough variant asthma. I was prescribed Singulair and that has been very helpful with my symptoms but I have had some side effects. My doctor switched me to Pulmicort I used it for about two ½ weeks that help my cough but did not help my breathing at all. So I went back on Singulair and the problems improved. My doctor also prescribed me Albuterol this did help some but does not seem to be as effect as what I would expect if it were asthma.
I recently noticed a tightness feeling in my throat. I have no wheezing or voice changes when my troubles occur. I was researching different causes and came up with Vocal Cord Dysfunction. Would that explain some of the symptoms like dry cough, chest tightness and possible the tightness in the right side the throat and might explain why the inhalers I have tried are not as effected as Singulair a pill?
I question the diagnosis of asthma do the normal lung function test and the fact my symptoms occur mostly during the day how every why Singulair is so effected makes me unsure.
Does Vocal Cord Dysfunction sound like a possible cause? Or does this sound like asthma? Or both?
What other causes might explain these symptoms?
How can you tell the difference between vocal cord dysfunction and Asthma?

[National Jewish Health]

Vocal cord dysfunction (VCD) could be associated with cough, chest tightness and "tightness" of the throat.  Usually a person with VCD feels more resistance to breathing in than to breathing out; just the opposite of asthma.

The normal pulmonary function tests (PFTs) do not rule out the diagnosis of asthma; nor does the seeming improvement with Singulair® (montelukast sodium) confirm it.  And, VCD does not improve with Singulair® (montelukast sodium), but Singulair® (montelukast sodium) can relieve a number of allergic diseases of the nose.  The diagnosis of asthma is often established with the performance of an inhalation challenge test; specifically, with a methacholine challenge.  You should ask your doctor about this test.

There are other causes of chronic cough and chest tightness that might be seen on a chest x-ray or a CT scan of the lungs.  Also, one can have silent reflux, without heartburn, which is unresponsive to antacids.  Your doctor might want to more carefully check you for reflux, with a test called a pH probe.