Every night when i lay down to go to bed i have so much throat clearing with phlegm. this only happens at night. why? what can i do? thank you.

Sinus problem: The most likely cause of your phlegm is where sinus content drips into your throat because when you lay down, it is easier for your sinus and nose content to drop down the back of your throat than out of your nose. This can be from allergy or infection and you describe frequent so likely allergic. The use of a nasal antihistamine or steroid would help. Check with your doctor.