16 month old not sleeping

My son is 16 months old. I normally nurse and rock him until hes really almost asleep then we lay together until he falls asleep. he normally would wakes up every 2-4 hours before midnight when I go into bed with him but for the last 2 weeks he wont fall asleep without me holding him and I cant put him down if I do he wakes up screaming. Hes getting all 4 of his first molars. Is this a phase? Will he sleep better after his teeth pop through? Anything I can do? I'm very against cio. Right before this he slept from 9pm-4am two nights in a row I was hoping that would be our new normal then this happened.