Runny nose in the morning only with white rubbery mucus. what could be the reason for this?

Could be allergies. Frequently, bedding and bed materials collect dust and dust mites which can make allergies worsen during sleep. Try washing all bedding in Hot water and wrap the actual mattress in a protective cover that seals in the dust and mites, so that you are not breathing them at night. You can also try using an antihistamine at night such as loratadine, cetirizine or fexofenadine.