night terrors and sleep regression

Going on week 4 of our 4 month old waking up every 2 hours. I've ended up nursing him to sleep most nights just so we can all get some rest. Up until last month he would do a 6 hour stretch. Lately he is going down for anywhere from 40 min to an hour when we do bedtime - then screaming bloody murder and crying for anywhere from 40 min to an hour before we can get him back down. I breastfeed and he gets one bottle a dAy which my husband gives. Normal diapers and we always make sure he burps well so don't think it's gas/ reflux. Perhaps bad dreams? It's heartbreaking. And hard work :/ anyone in the same boat and any tips?