I am sorry you are in such discomfort, and I hope I can give you some advice and guidance. However I need more information to help you. Are you a smoker or are you around chemicals at all? Were you sick before this cough started? You say lying down makes it worse...does anything else make it worse (or better)? Do you have any other symptoms or is it JUST this cough?
Thank you for that information,
Because this cough happened after a sinus infection, its likely that is to blame for your cough. One of the most common causes of a chronic cough is a post nasal drip, and that can indeed happen after a sinus infection. Another possibility is chronic sinusitis...as that can create a cough that is worse at night as yours seems to be. However, you would in all likelihood if this were the case still be feeling some cold symptoms.
Heartburn is also a very common cause of a cough, but I see you did try Nexium for that.
As you had a sinus infection it is likely (as the structures) are so close that it affected your ear and eustachian tube. One cause of a cough is something in your ear that irritates it. If you havent had someone check your ears, thats a possibility to consider....though usually its a foriegn body like a hair or some such.
Have you seen a specialist yet? An ENT is one who specializes in disorders of the ear, nose, and throat. It may be worthwhile to get his/her input and suggestions. He/she may want to visualize your larynx to see if the problem lies there if more common causes have been ruled out.
I hope I was able to help,
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