My baby use dto sleep 6-7 hours straight without waking up. Some ppl say to put him to sleep by 8pm.?

But i think its too early. Now he wakes up every 3-4 hours. what am i doing wrong. Also he stopped sleeping throughout when he started teething it just doesn't make sense when he's not teething that night. I started just putting back his pacifier and touching and speaking softly so he'll go back to bed, and it worked last night, but then around 5 am i had to give him milk. what tips can you give me so that he have sleep through like he used to.