What would cause you to have a thick clear to white mucus in your throat if sinuses and chest x-rays are normal.only happens after eating, laying dwn?

GERD: Reflux can cause that. Try an antacid for a couple of weeks and see if it goes away.

Look at diet: Certain foods in your diet can produce phlegm, which is basically mucus. Sweet foods, chocolates, desserts, breads, pasta, anything with gluten, can do this. So you may need a clinical nutritionist to intervene, and help you. Also, not having enough hydration can potentially cause it. Work with your doctor to address this, and you'll be satisfied.