Why is this happening??

Liz

My 4 month old just started out of nowhere waking up every 1-2 hours at night.. he usually does a good 6-7 hour stretch and sometimes sleeps through the night... 4 month sleep regression started weeks ago and he was waking frequently but then not that long ago he went back to his longer stretches... so what’s going on now ?? So confused!! He is getting over a cold that started last Saturday but he was sleeping just fine until last night 😭😭😭