yeah, teething will do that to a baby. the excessive saliva drains down into their tummies and makes their tummies upset.... can also cause diarrhea too.... and we're talking the real bad acidic kind of diarrhea, so make sure you're using diaper cream. and if his teeth are getting ready to break through, he may
not want your finger in his mouth because his gums might be really tender.
teething tablets work for immediate, short term relief, and motrin works for long term relief. let him sleep at an incline, and during the day, give him cold teething toys to chew on.
as far as how long his gums have been swollen.... it took my daughter at least a month and a half for her first tooth to break through!