It's been about four month. when i getup, i have running nose. then , after some hours, i again feel normal. is this some kind of allergy?

Yes: Many people have allergies to something in their bed. The most common cause is dust mites. Start by changing bedding, then vacuum around / under the bed and room to remove all dust. After that, use the beater bar of your vacuum to vacuum your mattress. Then flip the mattress over and vacuum it again. No kidding! flakes of skin shed and get caught in the bed. Dust mites live on that shed skin.

Can't tell: Perhaps the discharge is from accumulation of fluid in the sinuses when you are lying down. See your doctor since this is not normal.