Hello,I am so sorry your boy is having trouble.
Without seeing him I can not say with 100% certainty but it sounds like your boy has a problem with the salivary gland.
These glands can become infected, clogged or damaged, a hands on exam will be needed to find the cause.
Read more here
In cases of infected or clogged glands often medication and draining the build up of saliva is effective treatment, however in some cases the gland needs to be removed.
I would suggest having him seen by your vet tomorrow this is not something that will resolve on its own.
I hope all goes well, please reply back if you have additional questions or concerns