Can post nasal drip cause asthma? secondly, can it cause chronic need for throat clearing? thanks

No and yes: A post nasal drip will not cause asthma but it certainly could cause you to have to clear your throat. Everyone has a post nasal drip and it is only a problem when there is a change in either the quality or the quantity of the mucus. Once the cause of the change in mucus is treated the sensation of a post nasal drip should improve.