Как помочь 5-летнему сыну с необъяснимыми истериками?

Moms I need advice, im going to try to give the briefest explanation I can but I just don't know what to do anymore and an hoping someone has been through it and has some wisdom to share.

My 5 year old step son has something going on, he hasn't been diagnosed with anything yet but there's something there. What I'm lost on: he goes into these crying fits, they come out of no where, he won't answer us (my husband, myself or nana) what is wrong (i.e. if something hurts, if he's sad about something, if something is bothering him) he will just sit there staring at us and crying. Ive tried talking to him, holding him, if you can think of it ive probably tried it. But it has me at a breaking point. He has now been in his room just crying/screaming for about an hour now and I feel like I have no more options but to ignore him and let him get it out. Have any other moms been through this? Did you find something that worked? I want to help him but I don't know how to.

Note: he has bad behavioral problems - he has seen a neurologist, cardiologist, developmental specialist and behavioral specialist. The first two just to make sure everything was fine there and that wasn't causing anything. And the last two didn't really help much with whats going on. His mother's side of the family does have a history of bipolar could it be a precursor to that ?