Sleeping problems with my 11 months old baby..?

my son has slept through the night before, when he was around 6 months he would sleep for at least 6 hours straight before waking up for a bottle, he's going to be 11 months in a week and his sleeping pattern is of a 2 months old newborn!! he wakes up at least 3 times a night, even after he's been fed he doesnt seem to be sleeping soundly, he keeps crying or whining, i know he was teething, his upper teeth just came through, but how long does this teething process goes on?? i'm exhausted