Dyspnea lying down

I have suffered with asthma for decades and from infancy - before the invention of Ventolin! My asthma is accompanied by noisy wheezing and only alleviated by using medicines and sitting backwards on an upright dining chair and leaning over the back of it. My asthma has historically never lasted more than 2-3 days and has become much better after being prescribed Symbicort inhalers a couple of years ago.

Recently however, I have been getting symptoms of breathlessness and coughing, with NO wheezing. This only gets better when I lie down flat! My asthma medication does not help, nor a course of antibiotics in case it was a chest infection. My doctor keeps saying it is probably my asthma but I have never experienced this before. It is lasting for weeks at a time and I am worn out! Help