Brutal sleep

Think it’s a combo of sleep regression and teething (or was- 4 teeth in 3 weeks 😭), but I have to co-sleep with him in order to get any sleep. On a good night he sleeps in his crib until 4:30, on a bad night he’s with me before I’ve gone to sleep for the night. Part of the problem is he’s a loud cryer and I don’t want him to wake up his sister- that’s happened twice this week and it’s my personal hell. I think we’re on week 3 or 4 of this and I just want to sleep.