My dad is experiencing the need to clear his throat at night when he gets in bed. Any ideas?

 It goes on all night and he gets no sleep. My dad has Gerd along with cancer. He has this urgent need to clear his throats when in bed. Sometimes a little phlegm will come up, but most of the time nothing. We have tried various remedies,but if they don't work immediately he stops using them. My mom says he tosses and turns all night. He has arthritis in his shoulders so if sleeping on his side his arms go to sleep. He will not lie on his back or stomach. He wants the doctor to prescribe sleeping pills which he won't and I don't want him to take. We had his throats examined by a specialist and while they confirmed he has Gerd no other abnormality was found other than a slight structure in the muscle at the base of his neck. They didn't feel it would cause him to cough endlessly all night.