It could be a multiple of things first of all you are now between 3000-4000 less chemicals going down your lungs and the body has to repair itself hence mukus also it could be that your sensitive to PG so maybe try a higher VG juice, the other thing and i'm no doctor so would say seek medical attention you may have a throat infection. It's so hard to know exactly why and we all have different reactions to giving up the straights, also as above you need to increase water intake when vape as it causes dehydration.