Hi when i lay on my left side i start to cough mucus and i have a stinging burning feeling when i've coughed.chest x-ray clear too??

Possible acid reflux: This sounds like an episode of acid reflux causing coughing. The most common cause of chronic cough can be due to asthma, Post nasal dripping (feels like fluid running behind your throat), or acid reflux. For reflux you could try to not eat a couple hours before bedtime (1-2 hours), try sleeping with slight incline (use a couple of pillows) or you could use some over the counter anti acid tablets